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Multi-Tap Voltage Divider Calculator

Design or analyze complete 2-tap and 3-tap resistor ladders for window comparators, voltage thresholds, and multiple reference voltages. Find practical standard resistor combinations and check worst-case tolerance and power.

Help

Number of taps

Solve for

Define target window by

Circuit and inputs

Vin

Limits

3.300 V–3.300 V

Target V1Target V2Approx. RtotalSets the resistance scale; exact value is not critical.

Ideal resistor values

R1: 39.39 kΩ
R2: 30.30 kΩ
R3: 30.30 kΩ

Ideal total: 100.0 kΩ
Targets: V1 2.000 V · V2 1.000 V

Recommended standard resistors

Recommended from nearby standard values to minimize worst-case output error using your entered limits and tolerance.

Resistor seriesResistor tolerance

Resistors	V1	V2	Rtotal	Worst-caseVx error	Use
R1 39.7 kΩR2 30.5 kΩR3 30.5 kΩ	1.999 V	999.5 mV	100.7 kΩ	16.8 mV	Selected
R1 39.2 kΩR2 30.1 kΩR3 30.1 kΩ	1.999 V	999.3 mV	99.40 kΩ	17.2 mV
R1 39.2 kΩR2 30.5 kΩR3 30.1 kΩ	2.004 V	995.3 mV	99.80 kΩ	19.5 mV
R1 39.7 kΩR2 30.1 kΩR3 30.5 kΩ	1.994 V	1.003 V	100.3 kΩ	22.0 mV
R1 39.2 kΩR2 30.1 kΩR3 30.5 kΩ	2.004 V	1.009 V	99.80 kΩ	22.6 mV

Resulting tap voltages

Based on the selected standard resistor set.

Worst case evaluates 16 complete Vin and resistor-tolerance states.

Result	Minimum	Nominal	Maximum
V1	1.983 V	1.999 V	2.015 V
V2	985.6 mV	999.5 mV	1.013 V
Vcenter	1.487 V	1.499 V	1.511 V
Vwidth	985.6 mV	999.5 mV	1.013 V

Total ladder resistance100.7 kΩDivider current32.77 µATotal power108.1 µW

Detailed resultsShowHide

Selected resistors

R1: 39.70 kΩ
R2: 30.50 kΩ
R3: 30.50 kΩ

Ideal resistors

Ideal R1: 39.39 kΩ
Ideal R2: 30.30 kΩ
Ideal R3: 30.30 kΩ

Resistance and current

Actual Rtotal: 100.7 kΩ
Approx. Rtotal: 100.0 kΩ
Difference: +700 Ω
Divider current: 32.77 µA

Supply

Vin minimum: 3.300 V
Vin nominal: 3.300 V
Vin maximum: 3.300 V

Quantity	Target	Minimum	Nominal	Maximum	Nominal error	Worst-case error
V1	2.000 V	1.983 V	1.999 V	2.015 V	−993.0 µV	16.79 mV
V2	1.000 V	985.6 mV	999.5 mV	1.013 V	−496.5 µV	14.38 mV
Vcenter	1.500 V	1.487 V	1.499 V	1.511 V	−744.8 µV	12.59 mV
Vwidth	1.000 V	985.6 mV	999.5 mV	1.013 V	−496.5 µV	14.38 mV

Resistor power ratings

T_a— max ambient temperature°CHighest expected air temperature near the resistors.Default: 25 °C

R1 — suggested power rating1/32 WPmax: 43.24 µWR2 — suggested power rating1/32 WPmax: 33.34 µWR3 — suggested power rating1/32 WPmax: 33.34 µW

Based on the selected assumptions. Check the resistor datasheet for applicable limits.

Margin and derating settingsDefaultsShowHide

K_u— utilization factor%Maximum power dissipation is limited to 50% of the temperature-adjusted rating.T_ref— reference temperature°CFull rated power is assumed available through this temperature.T_zero— zero-power temperature°CThe generic linear approximation reaches zero usable power here.

Rating calculationsShowHide

The minimum required rating is Pmax ÷ (K_u × K_t). The calculator then selects the smallest supported common rating that is equal to or greater than that requirement.

K_t temperature factor100%

Resistor	Minimum rating	Suggested rating
R1	86.5 µW	1/32 W
R2	66.7 µW	1/32 W
R3	66.7 µW	1/32 W

1/32 W is the smallest power rating in the calculator’s list.

Resistor ladder formulas and examples

Analyze a 2- or 3-tap ladder from entered resistors, or choose standard resistor combinations from target voltages. Resistors are numbered from Vin toward Return; V1 is the highest tap. The complete operating instructions and theory follow in expandable sections.

Practical window comparator reference example

Select 2 taps, solve for R1, R2, R3, and define the window by Vcenter, Vwidth. Set Vin = 3.300 V ±1% (3.267–3.333 V), Vcenter = 1.500 V, Vwidth = 200 mV, Approx. Rtotal = 100 kΩ, E96 and resistor tolerance ±1%. The target thresholds are V1 = 1.600 V and V2 = 1.400 V. The ideal resistors are approximately 51.515 / 6.061 / 42.424 kΩ; those are distinct from standard-value recommendations.

For this example, require each tap to stay within ±3% of its target: V1 = 1.552–1.648 V and V2 = 1.358–1.442 V. This is an illustrative design requirement to compare with the results, not an additional calculator control. The first row is selected automatically; Use selects an alternative.

Window comparator reference. Replaces current calculator inputs.

Two nearby E96 ladders, with supply and resistor limits

Quantity	First recommendation	Second recommendation
R1 / R2 / R3 (kΩ)	52.3 / 6.04 / 43.2	51.1 / 6.04 / 42.2
Nominal Rtotal / current	101.54 kΩ / 32.4995 µA	99.34 kΩ / 33.2192 µA
V1 nominal (min–max), V	1.600276 (1.567958–1.632933)	1.602496 (1.570155–1.635177)
V2 nominal (min–max), V	1.403979 (1.373991–1.434337)	1.401852 (1.371892–1.432183)
Vcenter nominal (min–max), V	1.502127 (1.471791–1.532782)	1.502174 (1.471857–1.532809)
Vwidth nominal (min–max), mV	196.297 (190.710–202.022)	200.644 (194.939–206.491)
Largest worst-case threshold error	34.337 mV	35.177 mV
Both taps within illustrative ±3% requirement?	Yes	Yes

Both ladders meet this tap-voltage requirement. The first ranks higher because its largest worst-case V1/V2 target error is smaller. The second is closer to both 100 kΩ and a nominal 200 mV window, so it can remain a reasonable stocked alternative. Window-mode ranking prioritizes the target thresholds, rather than independently optimizing center and width. This is ranking among supported nearby candidates, not proof of a global optimum or stock availability.

Center and width bounds come from all 16 complete supply/resistor endpoint states. Compute them together at each state; subtracting unrelated V1/V2 extremes would overstate window variation. Taps are assumed high impedance. Check loading, selected-part power and voltage ratings in the actual circuit; window spacing is not comparator hysteresis.

Three-tap analysis example

Select 3 taps and solve for V1, V2, V3. Enter Vin = 5 V and R1 / R2 / R3 / R4 = 10 / 20 / 30 / 40 kΩ. For the nominal values, Rtotal = 100 kΩ, current = 50 µA, and the taps are 4.5 / 3.5 / 2 V. Loading this nominal example sets supply and resistor tolerances to zero. Set the limits to match the real components when evaluating the full ranges.

Three-tap nominal analysis. Replaces current calculator inputs.

Taps are assumed to have high input impedance. The model does not directly include tap loading, comparator input bias current or feedback. Check these effects in the actual circuit.

How calculations are checked

Automated checks compare known two- and three-tap ladders, ideal inverse solutions, correlated tolerance states, window calculations, standard-ladder ranking and resistor power assumptions with expected results. The About page describes the original spreadsheet and hand-calculation process. These checks verify the circuit model; they are not physical component measurements.

Explore calculator features and benefits →

For one reference node, use the voltage divider calculator.

How to use

Show

Quick Start

Choose the number of taps, then use Solve for to tell the calculator whether you know the resistor values or the voltages you want.

2 taps — solve for V1, V2

Select 2 taps.
Under Solve for, select V1, V2.
Enter Vin, R1, R2, and R3.
Set the Vin Limits and resistor tolerance.
Review the calculated V1 and V2 values in Resulting tap voltages.
Review Vcenter, Vwidth, divider current, and resistor power as needed.

Use this mode when the resistor values are already known and you want to determine the resulting window or tap voltages.

2 taps — solve for R1, R2, R3

Select 2 taps.
Under Solve for, select R1, R2, R3.
Enter Vin and its Limits.
Under Define target window by, choose either V1, V2 or Vcenter, Vwidth.
Enter the desired target voltages.
Enter Approx. Rtotal to set the desired resistance scale.
Review the calculated Ideal resistor values.
Under Recommended standard resistors, select the desired resistor series and tolerance.
Review the recommended resistor combinations.
The first combination is selected automatically. Select Use on another row to analyze a different combination.
Review Resulting tap voltages, Detailed results, and Resistor power ratings.

Approx. Rtotal sets the general resistance scale. It is not treated as an exact target; voltage accuracy is the primary design objective.

Define by V1, V2

Use V1, V2 when the upper and lower reference voltages are already known.

Example: Target V1 = 2.000 V and Target V2 = 1.000 V.

Define by Vcenter, Vwidth

Use Vcenter, Vwidth when the desired window is easier to describe by its midpoint and total width.

V_center = V₁ + V₂2

V_width = V₁ − V₂

The schematic shows Vwidth between V1 and V2 and Vcenter at the midpoint.

Example: Vcenter = 1.500 V and Vwidth = 200 mV correspond to V1 = 1.600 V and V2 = 1.400 V.

3 taps — solve for V1, V2, V3

Select 3 taps.
Under Solve for, select V1, V2, V3.
Enter Vin, R1, R2, R3, and R4.
Set Vin Limits and resistor tolerance.
Review the calculated V1, V2, and V3 values.
Review divider current and resistor power as needed.

Use this mode when the four resistor values are known and you want to calculate all three tap voltages.

3 taps — solve for R1, R2, R3, R4

Select 3 taps.
Under Solve for, select R1, R2, R3, R4.
Enter Vin and its Limits.
Enter Target V1, Target V2, and Target V3.
Enter Approx. Rtotal.
Review the calculated Ideal resistor values.
Select the resistor series and tolerance under Recommended standard resistors.
Compare the recommended standard-resistor combinations.
Use Use to select an alternative combination if desired.
Review Resulting tap voltages, Detailed results, and Resistor power ratings.

For three taps, the target voltages must satisfy V1 > V2 > V3.

Calculator features and benefits

Most voltage-divider calculators solve for a single output. This calculator designs or analyzes an entire 2-tap or 3-tap resistor ladder, making it easier to create multiple related reference voltages from one supply.

Design multiple thresholds together

Calculate two or three related tap voltages as one circuit instead of solving several divider equations separately.

Design a window comparator

For two taps, define the desired window using either V1/V2 or Vcenter/Vwidth.

Find practical standard resistors

Calculate the ideal resistor values, then search All E-Series, E24, E48, E96, or E192 for practical combinations.

Optimize the complete ladder

The calculator evaluates resistor combinations as complete circuits instead of simply rounding each ideal resistor independently.

Check worst-case performance

Vin limits and resistor tolerance are evaluated together so minimum and maximum tap voltages represent complete physical circuit states.

Verify resistor power

Calculate resistor dissipation and recommended ratings using configurable margin and temperature derating.

This is useful for window comparators, multi-level threshold detectors, ADC thresholds, supervisory circuits, and other designs that need multiple related reference voltages from one resistor ladder.

Advanced Features

Expand a topic below for more information about the calculator's design and analysis features.

Vin limitsShow

Vin does not need to be treated as an exact voltage. Use Limits to specify the expected minimum and maximum supply voltage.

The calculator supports the same Vin-limit formats as the Voltage Divider Calculator:

±%
+% / −%
±V
+V / −V

Vin minimum and maximum values are included in the worst-case calculations together with resistor tolerance.

Standard resistor selectionShow

When solving for resistor values, the calculated ideal resistances usually do not correspond exactly to standard resistor values.

Select:

All E-Series
E24
E48
E96
E192

All E-Series searches the supported preferred values across all available series and is the default.

Open E-series reference below

Recommended resistor alternativesShow

The calculator evaluates nearby standard resistor combinations and ranks them by electrical performance.

The calculator ranks combinations primarily by worst-case voltage accuracy, followed by nominal accuracy and then closeness to Approx. Rtotal. The first row is the highest-ranked recommendation and is selected initially.

Select Use on another row to make that combination active. Changing the selected combination updates:

Resulting tap voltages
Detailed results
Resistor power ratings

Row order continues to show recommendation ranking even when a different row is selected.

See How resistor combinations are ranked below the recommendation table for details.

Worst-case tolerance analysisShow

The calculator evaluates complete combinations of resistor tolerance and Vin limits rather than treating each output independently.

For two taps, three resistors produce 8 resistor-limit combinations. Including minimum and maximum Vin produces 16 complete states.

For three taps, four resistors produce 16 resistor-limit combinations. Including minimum and maximum Vin produces 32 complete states.

This preserves the relationship between the tap voltages. For a 2-tap design, Vcenter and Vwidth are calculated from each complete state rather than by combining unrelated V1 and V2 extremes.

See Theory & formulas for details

Detailed resultsShow

Expand Detailed results below the calculator to inspect the currently selected resistor combination in more detail.

Depending on the selected mode, the section shows:

Selected standard resistors
Ideal resistor values
Actual and approximate Rtotal
Divider current
Vin minimum, nominal, and maximum
Voltage targets
Minimum, nominal, and maximum results
Nominal error
Worst-case error

Detailed results always reflect the resistor combination currently marked Selected in the recommendation table.

Vcenter and VwidthShow

In a 2-tap design, V1 and V2 define a voltage window.

V_center = V₁ + V₂2

V_width = V₁ − V₂

Vwidth is the spacing between the two fixed reference voltages. It is not comparator hysteresis; hysteresis normally requires feedback that changes a comparator's switching threshold.

See Theory & formulas for the complete derivation

Resistor power ratingsShow

The calculator determines the worst-case power dissipated by each resistor and recommends a common resistor power rating.

Ta — max ambient temperature is the main environmental input.

Additional assumptions are available under Margin and derating settings:

Ku — utilization factor
Tref — reference temperature
Tzero — zero-power temperature

Open power-rating reference below

Tap loading and comparator inputsShow

The calculator assumes the tap loads have sufficiently high input impedance that they do not materially change the resistor-ladder voltages.

Comparator input bias or leakage current may become important with:

High-value resistor ladders
Tight voltage tolerances
Comparators with higher input bias current
Elevated temperatures

See Theory & formulas for the approximate bias-current error relationship and additional assumptions.

Reset and defaultsShow

Reset restores the calculator's default example and design assumptions:

Number of taps: 2 taps
Solve for: R1, R2, R3
Define target window by: V1, V2
Vin: 3.300 V
Vin Limits: ±0%
Target V1 / V2: 2.000 V / 1.000 V
Approx. Rtotal: 100 kΩ
Resistor series: All E-Series
Resistor tolerance: ±1%
Power-rating assumptions: Ta = 25 °C, Ku = 50%, Tref = 70 °C, and Tzero = 125 °C

Reset also returns the recommendation to the highest-ranked resistor combination.

Back to calculator ↑

Theory & formulas

Show

Definitions

A multi-tap voltage divider is a series resistor ladder that creates two or three intermediate voltages from a single input voltage.

Term	Definition
Vin	Input voltage applied across the resistor ladder
V1, V2, V3	Tap voltages, measured relative to Return
R1, R2, R3, R4	Series resistors, numbered from Vin toward Return
Rtotal	Total resistance of the resistor ladder
Idiv	Current flowing through the unloaded resistor ladder
Vcenter	Midpoint voltage between V1 and V2
Vwidth	Voltage difference between V1 and V2
Return	Bottom reference node of the resistor ladder
Pmax	Highest calculated resistor power over the evaluated Vin and resistance limits

For a 2-tap divider, the ladder contains R1, R2, and R3.

For a 3-tap divider, the ladder contains R1, R2, R3, and R4.

Series ladder operation

With no significant load connected to the taps, the same current flows through every resistor.

Two taps

R_total = R₁ + R₂ + R₃

Three taps

R_total = R₁ + R₂ + R₃ + R₄

I_div = V_inR_total

Each tap voltage is determined by the resistance between that tap and Return.

Two-tap divider

V₁ = V_inR₂ + R₃R₁ + R₂ + R₃

V₂ = V_inR₃R₁ + R₂ + R₃

0 < V₂ < V₁ < V_in

For a window comparator, V1 and V2 can be used as the two fixed reference thresholds.

Three-tap divider

V₁ = V_inR₂ + R₃ + R₄R₁ + R₂ + R₃ + R₄

V₂ = V_inR₃ + R₄R₁ + R₂ + R₃ + R₄

V₃ = V_inR₄R₁ + R₂ + R₃ + R₄

0 < V₃ < V₂ < V₁ < V_in

Designing from target voltages

Target voltages determine the resistor ratios, but they do not uniquely determine the absolute resistor values. Multiplying every resistor in the ladder by the same factor leaves the tap voltages unchanged.

Approx. Rtotal establishes the desired resistance scale. The calculator uses it to determine the corresponding ideal resistor values.

Two taps

R₁ = R_totalV_in − V₁V_in

R₂ = R_totalV₁ − V₂V_in

R₃ = R_totalV₂V_in

Three taps

R₁ = R_totalV_in − V₁V_in

R₂ = R_totalV₁ − V₂V_in

R₃ = R_totalV₂ − V₃V_in

R₄ = R_totalV₃V_in

The resulting ideal resistor values usually are not exact standard resistor values. The calculator therefore searches practical E-series combinations near the ideal solution.

Open E-series reference below

Window center and width

For a 2-tap divider, the same target window can be specified using either V1 and V2 or Vcenter and Vwidth.

V_center = V₁ + V₂2

V_width = V₁ − V₂

Reverse conversion

V₁ = V_center + V_width2

V₂ = V_center − V_width2

Vwidth is not comparator hysteresis. V1 and V2 are two fixed reference voltages. Comparator hysteresis normally uses feedback so that a comparator's switching threshold changes depending on its output state.

Window design example

Open the worked window design example.

Three-tap example

Open the worked three-tap analysis example.

Standard resistor selection

Real designs normally use standard resistor values rather than the exact ideal values.

The calculator searches nearby values from the selected resistor series:

All E-Series
E24
E48
E96
E192

When All E-Series is selected, the calculator searches the supported preferred values across all of these series.

The search evaluates resistor combinations as complete circuits rather than simply rounding each ideal resistor independently. Candidate combinations are compared by their resulting circuit performance, not simply by how close each resistor is to its ideal value. This allows the error from one resistor to compensate for another and can produce a more accurate overall set of tap voltages.

Combinations are ranked by:

Lowest maximum worst-case target-voltage error
Lowest maximum nominal target-voltage error
Lowest combined nominal target-voltage error
Closest total resistance to Approx. Rtotal
Lower maximum resistor power as the final tie-breaker

For V1/V2 and 3-tap designs, these error metrics use the requested tap voltages directly. In Vcenter/Vwidth mode, the requested window is converted to target V1 and V2 thresholds before candidates are ranked. Vcenter and Vwidth remain correlated in the displayed tolerance results, but they are not separate sorting terms.

Approx. Rtotal is secondary to voltage accuracy. The calculator does not choose a less accurate combination only because its total resistance is closer to the requested value.

Open E-series reference below

Tolerance and worst-case analysis

Resistor tolerance changes the actual resistance values, and Vin limits change the voltage applied to the ladder. The calculator evaluates these limits together as complete circuit states.

Two taps

2³ = 8

resistor-limit combinations.

Including minimum and maximum Vin:

8 × 2 = 16

complete states.

Three taps

2⁴ = 16

resistor-limit combinations.

Including minimum and maximum Vin:

16 × 2 = 32

complete states.

For every complete state, the calculator recalculates all tap voltages.

This preserves the correlation between V1, V2, Vcenter, and Vwidth.

For example, the calculator does not determine worst-case Vwidth by combining the maximum V1 from one resistor state with the minimum V2 from a different state.

Instead:

V_width = V₁ − V₂

is calculated for every complete state, and the actual minimum and maximum Vwidth are then determined from those states.

Resistor power

The nominal power dissipated by each resistor is:

P_n = I_div²R_n

Because Vin and resistance can vary, the calculator also determines Pmax, the highest resistor dissipation found across the evaluated worst-case states.

The suggested resistor rating accounts for maximum ambient temperature, utilization margin, and temperature derating.

P_rating,min = P_maxK_uK_t

Ku — utilization factor
Kt — temperature derating factor

The calculator then selects the smallest supported common resistor power rating that meets or exceeds the required rating.

Open power-rating reference below

Input loading and comparator bias current

The calculator assumes that devices connected to the voltage taps have sufficiently high input impedance that they do not significantly load the resistor ladder.

V_error ≈ I_biasR_TH

Here, RTH is the Thevenin resistance looking back into the divider from the tap.

Input bias or leakage current is often small with modern CMOS comparator inputs and moderate resistor values, but it can become important with:

High-value resistor ladders
Higher comparator input bias or leakage current
Tight threshold requirements
Elevated temperatures

Check the comparator datasheet when these effects may be significant.

Assumptions and limitations

The calculator is intended for DC resistor-ladder design and makes the following assumptions.

DC steady-state operation.
Tap loads have sufficiently high input impedance that they do not materially load the divider.
One selected resistor tolerance applies to all divider resistors.
Vin variation is represented by the configured minimum and maximum Vin limits.
The bottom of the ladder is connected to Return at 0 V.
Standard resistor recommendations use the supported E-series values.
Power-rating calculations use the CircuitKitchen generic linear derating model and selected margin assumptions.

The calculator does not currently model:

Comparator input bias current directly
Comparator input capacitance
Explicit load resistance at individual taps
Comparator hysteresis or positive-feedback networks
Resistor temperature coefficient
Statistical/RSS tolerance analysis
Noise
AC behavior
RC filtering
Non-zero bottom reference voltage

If these effects are significant in the application, include them in the final circuit analysis.

Back to calculator ↑

E-series resistor values

Show

E-series are standardized sets of preferred nominal resistance values defined by IEC 60063. They provide a consistent selection of values for circuit design and component manufacturing.

The nominal resistance is the specified value of a resistor. Its actual resistance may differ within its stated tolerance. The E-series identifies a set of nominal values; tolerance describes the permitted variation around a selected value.

Values per decade

The number following E indicates how many unique nominal values the series contains per decade. A decade spans a factor of ten, such as 100 Ω to below 1 kΩ or 1 kΩ to below 10 kΩ.

E6, for example, contains these six values between 1 kΩ and 10 kΩ: 1.0 kΩ, 1.5 kΩ, 2.2 kΩ, 3.3 kΩ, 4.7 kΩ, and 6.8 kΩ.

The pattern repeats in other decades by multiplying or dividing by powers of ten. The 10 kΩ boundary begins the next decade, so it is not counted twice.

Series and commonly associated tolerances

Series	Values per decade	Significant digits	Commonly associated tolerances
E3	3	2	No tolerance association listed in the cited Vishay table
E6	6	2	±20%
E12	12	2	±10%
E24	24	2	±5%
E48	48	3	±2%
E96	96	3	±1%
E192	192	3	±0.5%, ±0.25%, ±0.1%

These are conventional associations, not limits on the tolerances available for each value. Manufacturers offer preferred values at multiple tolerances, depending on the product family, resistance range, and package. Check the component datasheet for available combinations.

For example, a nominal 10 kΩ resistor with ±1% tolerance has resistance limits of 9.90 kΩ and 10.10 kΩ under the specified datasheet conditions.

R_min = R_nominal × (1 − t) R_max = R_nominal × (1 + t)

Use 0.01 for ±1%. E3, E6, E12, and E24 form one nested group. E48, E96, and E192 form another. E24 is not fully contained in E192: for example, E24 includes 2.2 kΩ, while E192 includes nearby 2.21 kΩ.

All E-series

All E-series searches every preferred resistance value in E24, E48, E96, and E192, with duplicates removed. This also includes E3, E6, and E12 values.

The combined set contains 205 unique values per decade. It is formed by combining E24 and E192, which together cover all the series listed above.

Choose this option for the broadest selection of values supported by the calculator, then check your distributor for components with the required tolerance, ratings, availability, and price. If a suggested component is unavailable or unsuitable, evaluate another suggested value or an available value from the distributor’s catalog.

All E-series is a calculator search category, not a separate standardized E-series. It does not include every custom or nonstandard resistance sold by manufacturers, and it does not guarantee that a particular component is stocked.

Choosing preferred values

Choose All E-series when you want a broad search and plan to source components from a distributor. Choose an individual series when you want to match an existing inventory or a manufacturer’s product range.

Select tolerance separately. The preferred-value set determines which nominal resistances are considered; tolerance determines the resistance variation used in the calculations.

A closer nominal match does not necessarily produce the best worst-case circuit performance. Compare the calculated circuit results with the selected values and tolerances, as well as the component ratings.

A practical resistor-selection workflow

Define the circuit requirements. Establish the desired resistance or circuit output, acceptable error, operating conditions, and relevant size, voltage, and power constraints.
Calculate the ideal value. Determine the resistance that would produce the desired result with ideal components.
Select preferred values and tolerance. Choose All E-series for a broad search, or an individual series to match your sourcing requirements. Set the tolerance you intend to purchase.
Compare circuit performance. Review nominal and worst-case results using the suggested values. Check resistor power dissipation and the recommended power rating. For resistor combinations, evaluate the complete circuit as well as each resistor.
Find suitable components. Search a distributor’s catalog for the selected resistance and tolerance. Check package, rated power and derating, temperature coefficient, voltage rating, stock, lead time, and price at your required quantity. Check pulse capability when applicable.
Evaluate alternatives when necessary. If a component is unavailable or unsuitable, consider another suggested value or enter an available value into the calculator. Recalculate with the tolerance of the actual component you intend to buy.
Specify the selected component. Record the manufacturer’s part number and relevant specifications in the bill of materials. Verify the datasheet ratings and operating conditions before finalizing the design.

The goal is to select components that meet the circuit requirements and can be sourced at an acceptable price. The closest nominal resistance is a useful starting point; the final selection also depends on tolerance, operating limits, and availability.

E-series and component price

A larger E-series does not automatically mean a higher component price. Different resistance values within the same product family may have identical or similar prices, while particular values can differ in price, stock, or lead time.

Compare actual components with the same relevant specifications, purchase quantity, and packaging. Use the calculator to evaluate electrical performance and the distributor’s catalog to confirm purchasing options.

How preferred values are spaced

E-series values follow approximately equal percentage steps rather than equal differences in ohms. For a series with N values per decade, the ideal adjacent-value ratio is 10^1/N.

Ideal step = 100 × (10^1/N − 1)%

This is approximately 10.1% for E24 and 2.43% for E96. Actual tabulated steps vary because the standardized values use rounded numbers.

Use the published preferred-value tables when selecting components. The formula explains the approximate spacing; it does not replace the standardized tables.

Preferred-value tables

Each table lists every preferred value within one decade, normalized from 1 up to—but not including—10. Multiply an entry by a power of ten to obtain resistance values in other decades. For example, 4.7 represents 4.7 Ω, 47 Ω, 470 Ω, 4.7 kΩ, 47 kΩ, and so on. Inclusion in a table does not guarantee availability in a particular tolerance or package.

E3 — 3 values per decade

E6 — 6 values per decade

E12 — 12 values per decade

E24 — 24 values per decade

E48 — 48 values per decade

1.00
1.05
1.10
1.15
1.21
1.27
1.33
1.40
1.47
1.54
1.62
1.69
1.78
1.87
1.96
2.05
2.15
2.26
2.37
2.49
2.61
2.74
2.87
3.01
3.16
3.32
3.48
3.65
3.83
4.02
4.22
4.42
4.64
4.87
5.11
5.36
5.62
5.90
6.19
6.49
6.81
7.15
7.50
7.87
8.25
8.66
9.09
9.53

E96 — 96 values per decade

1.00
1.02
1.05
1.07
1.10
1.13
1.15
1.18
1.21
1.24
1.27
1.30
1.33
1.37
1.40
1.43
1.47
1.50
1.54
1.58
1.62
1.65
1.69
1.74
1.78
1.82
1.87
1.91
1.96
2.00
2.05
2.10
2.15
2.21
2.26
2.32
2.37
2.43
2.49
2.55
2.61
2.67
2.74
2.80
2.87
2.94
3.01
3.09
3.16
3.24
3.32
3.40
3.48
3.57
3.65
3.74
3.83
3.92
4.02
4.12
4.22
4.32
4.42
4.53
4.64
4.75
4.87
4.99
5.11
5.23
5.36
5.49
5.62
5.76
5.90
6.04
6.19
6.34
6.49
6.65
6.81
6.98
7.15
7.32
7.50
7.68
7.87
8.06
8.25
8.45
8.66
8.87
9.09
9.31
9.53
9.76

E192 — 192 values per decade

1.00
1.01
1.02
1.04
1.05
1.06
1.07
1.09
1.10
1.11
1.13
1.14
1.15
1.17
1.18
1.20
1.21
1.23
1.24
1.26
1.27
1.29
1.30
1.32
1.33
1.35
1.37
1.38
1.40
1.42
1.43
1.45
1.47
1.49
1.50
1.52
1.54
1.56
1.58
1.60
1.62
1.64
1.65
1.67
1.69
1.72
1.74
1.76
1.78
1.80
1.82
1.84
1.87
1.89
1.91
1.93
1.96
1.98
2.00
2.03
2.05
2.08
2.10
2.13
2.15
2.18
2.21
2.23
2.26
2.29
2.32
2.34
2.37
2.40
2.43
2.46
2.49
2.52
2.55
2.58
2.61
2.64
2.67
2.71
2.74
2.77
2.80
2.84
2.87
2.91
2.94
2.98
3.01
3.05
3.09
3.12
3.16
3.20
3.24
3.28
3.32
3.36
3.40
3.44
3.48
3.52
3.57
3.61
3.65
3.70
3.74
3.79
3.83
3.88
3.92
3.97
4.02
4.07
4.12
4.17
4.22
4.27
4.32
4.37
4.42
4.48
4.53
4.59
4.64
4.70
4.75
4.81
4.87
4.93
4.99
5.05
5.11
5.17
5.23
5.30
5.36
5.42
5.49
5.56
5.62
5.69
5.76
5.83
5.90
5.97
6.04
6.12
6.19
6.26
6.34
6.42
6.49
6.57
6.65
6.73
6.81
6.90
6.98
7.06
7.15
7.23
7.32
7.41
7.50
7.59
7.68
7.77
7.87
7.96
8.06
8.16
8.25
8.35
8.45
8.56
8.66
8.76
8.87
8.98
9.09
9.20
9.31
9.42
9.53
9.65
9.76
9.88

All E-series — 205 values per decade

Combined E24 and E192 values, with duplicates removed.

1.00
1.01
1.02
1.04
1.05
1.06
1.07
1.09
1.10
1.11
1.13
1.14
1.15
1.17
1.18
1.20
1.21
1.23
1.24
1.26
1.27
1.29
1.30
1.32
1.33
1.35
1.37
1.38
1.40
1.42
1.43
1.45
1.47
1.49
1.50
1.52
1.54
1.56
1.58
1.60
1.62
1.64
1.65
1.67
1.69
1.72
1.74
1.76
1.78
1.80
1.82
1.84
1.87
1.89
1.91
1.93
1.96
1.98
2.00
2.03
2.05
2.08
2.10
2.13
2.15
2.18
2.20
2.21
2.23
2.26
2.29
2.32
2.34
2.37
2.40
2.43
2.46
2.49
2.52
2.55
2.58
2.61
2.64
2.67
2.70
2.71
2.74
2.77
2.80
2.84
2.87
2.91
2.94
2.98
3.00
3.01
3.05
3.09
3.12
3.16
3.20
3.24
3.28
3.30
3.32
3.36
3.40
3.44
3.48
3.52
3.57
3.60
3.61
3.65
3.70
3.74
3.79
3.83
3.88
3.90
3.92
3.97
4.02
4.07
4.12
4.17
4.22
4.27
4.30
4.32
4.37
4.42
4.48
4.53
4.59
4.64
4.70
4.75
4.81
4.87
4.93
4.99
5.05
5.10
5.11
5.17
5.23
5.30
5.36
5.42
5.49
5.56
5.60
5.62
5.69
5.76
5.83
5.90
5.97
6.04
6.12
6.19
6.20
6.26
6.34
6.42
6.49
6.57
6.65
6.73
6.80
6.81
6.90
6.98
7.06
7.15
7.23
7.32
7.41
7.50
7.59
7.68
7.77
7.87
7.96
8.06
8.16
8.20
8.25
8.35
8.45
8.56
8.66
8.76
8.87
8.98
9.09
9.10
9.20
9.31
9.42
9.53
9.65
9.76
9.88

Sources

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Resistor power ratings and derating

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What the rating means

A resistor converts electrical power into heat. Its dissipation is the power produced by the circuit; its rated or nameplate wattage is the manufacturer's allowed dissipation under specified temperature and mounting conditions. A 1/4 W resistor does not always dissipate 1/4 W, and its full rating may not be available in a hot enclosure or with different mounting conditions.

For one operating point, resistor dissipation can be calculated as P = V_R × I = I² × R = V_R² / R, where V_R is the voltage across that resistor. Use volts, amperes, ohms, and watts in the equations: 10 mA = 0.010 A and 100 mW = 0.100 W. Evaluate each resistor separately; total network power does not determine each resistor's rating.

CircuitKitchen determines a power basis for each resistor, applies utilization margin and temperature derating, and selects the smallest supported wattage that meets the requirement. The suggestion is conditional on the entered circuit bounds and selected assumptions.

Determine the power basis

For continuous operation, P_basis is that resistor's maximum modeled continuous dissipation, P_max. Use the selected or entered resistor values and their limits, rather than only the ideal resistance or nominal circuit power.

Voltage Divider evaluates Rtop and Rbot separately over the entered supply, resistor, and applicable load limits. Its model also considers relevant intermediate resistance values that can produce a maximum between tolerance endpoints. Use the calculated Pmax for each resistor.

Multi-Tap evaluates each ladder resistor separately in complete combinations of supply and resistor-tolerance endpoints. At each evaluated state, P_i = I_ladder² × R_i. The reported maximum for each resistor supplies its rating calculation. The maximum-power states for different resistors need not be the same. Do not imply that this model searches intermediate resistance extrema or that it models loaded taps.

Parallel evaluates each branch at the specified voltage across the network. With a fixed voltage, P_i = V² / R_i, so the lowest resistance in that branch's tolerance range produces its highest power. Unequal resistances do not share power equally.

LED uses the series resistor's maximum modeled dissipation, accounting for supply limits, LED count and forward-voltage limits, enabled switch/driver drop, and resistor limits. In the fixed-drop model:

Vf is per LED; Vsw is the total enabled switch/driver drop and is zero when disabled. Use a consistent operating state. Do not combine If_max with an unrelated R_max to calculate power. These fixed-drop estimates do not model diode curves or changes in Vf with temperature automatically.

For Parallel's repeating rectangular pulses, use worst-case average power as the thermal basis:

Duty cycle D is a fraction. A 25% duty cycle is D = 0.25. The other calculators do not provide this pulse-rating calculation.

Temperature derating

Temperature derating reduces the fraction of nameplate wattage available at the selected temperature. CircuitKitchen uses a generic linear approximation:

T_a: highest expected local ambient temperature near the resistor.
T_ref: temperature through which the model allows full rated power.
T_zero: temperature at which the model allows zero power.
k_t: available fraction of nameplate power.

T_zero must exceed T_ref. Use finite, valid settings. When dissipation is positive and k_t = 0, increasing wattage cannot produce a suitable finite rating under this model; review the operating conditions or the appropriate component thermal model.

Use the highest expected local temperature, including enclosure heating, airflow, nearby components, and PCB heating. T_a is not automatically the resistor body's operating temperature. Some datasheets base ratings on terminal, case, or board temperatures and specific cooling conditions. Do not substitute those temperatures directly into an ambient model without establishing that the thermal assumptions apply. This calculator does not solve component self-heating or a complete thermal network.

Utilization margin

The utilization setting limits modeled dissipation to a chosen fraction of the temperature-adjusted rating. Lower utilization provides more margin but requires greater nameplate wattage. Use the percentage shown in the control as a fraction in arithmetic: k_u = Ku_percent / 100. A 50% setting means k_u = 0.50. Similarly, a displayed Kt of 100% means k_t = 1.00; some panels display Kt directly as a fraction.

These equations apply with positive valid k_u and k_t. A smaller utilization setting and a higher ambient temperature can independently increase the required rating. Utilization and temperature derating address different assumptions; the recommended wattage already includes both. Do not apply the same selected factors a second time.

Select a supported wattage

Choose the smallest supported rating equal to or above P_rated,min, never a lower rating. CircuitKitchen's supported list currently runs from 1/32 W through 5 W and includes intermediate ratings; use the calculator's actual list rather than assuming every step doubles. A suggested wattage is not a guarantee that a particular resistance, tolerance, package, and wattage combination is sold or stocked.

If the required rating exceeds the supported list, no listed rating meets the requirement. This differs from invalid input and from zero available power at the selected temperature. Review the circuit, cooling, component family, or required rating. For an LED state with no modeled resistor dissipation, preserve its "No dissipation predicted" result; this does not establish suitability under unmodeled conditions.

Defaults and worked examples

CircuitKitchen defaults are T_a = 25 °C, Ku = 50%, T_ref = 70 °C, and T_zero = 125 °C. They are initial calculator assumptions, not universal resistor specifications or a guarantee of safety. Choose settings appropriate to the actual component and operating environment.

At the defaults, k_t = 1.00 and k_u = 0.50. For P_basis = 100 mW:

The next supported wattage is 1/4 W, or 250 mW.

At T_a = 85 °C with the same T_ref, T_zero, utilization, and dissipation:

The next supported wattage is 1/3 W. Higher ambient temperature requires a higher rated component even though circuit dissipation has not changed.

For a Parallel pulse example, P_peak,worst = 1 W and D = 0.10 give P_basis = 0.10 W. At the default factors the minimum continuous rating is 0.20 W, suggesting 1/4 W thermally. This result alone does not establish pulse survivability.

Pulse limits and final component selection

A resistor may meet its average-power requirement and still exceed peak power, pulse width, pulse energy, repetition rate, repetitive pulse, working-voltage, or overload limits. For a rectangular pulse, energy per pulse is E = P_peak × t_on in joules. Check the manufacturer's pulse curves and conditions separately; do not infer allowable pulses from continuous wattage alone.

Use this workflow: review circuit bounds and each resistor's power basis; select realistic temperature and utilization assumptions; check the suggested wattage; then source an actual component and verify its datasheet. Check power and derating, mounting and PCB thermal conditions, maximum working voltage, overload and pulse limits, package, resistance, tolerance, and temperature coefficient. Verify thermal behavior in the intended assembly when needed. Keep LED and driver electrical and thermal limits separate from the resistor rating check.

Derating changes allowed dissipation. It does not model resistance drift, temperature coefficient, aging, or LED forward-voltage changes. A recommended rating is a design aid under the selected model, not a substitute for component specifications or thermal validation.

Sources

General rating and pulse guidance; the selected component’s datasheet controls its specifications.

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