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Voltage Divider Calculator

Select standard voltage-divider resistor values based on worst-case output error. Compare alternatives and evaluate voltage limits, loading effects, and resistor power ratings.

Help
Solve for:

Ideal circuit

Ideal voltage divider circuitUnloaded divider with Vin 3.30 V, Rtop 17.5 kΩ, Rbot 10.0 kΩ, and Vout 1.20 V.Vin3.30 VRtop17.5 kΩRbot10.0 kΩVout1.20 VReturn
Limits
17.50 kΩ
Limits

Recommended standard Rtop

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

Recommended value17.6 kΩ, 1/32 W (31.3 mW)

Resulting Vout range

Using recommended Rtop = 17.6 kΩ
Output voltage range and deviation from target
MeasurementMinNominalMax
Voltage1.180 V1.196 V1.211 V
Deviation from target (1.200 V)−1.63%−0.36%+0.91%
1.196 V nominal1.180 V–1.211 V with tolerances−1.63% to +0.91% from target

Vout nominal 1.196 V; range 1.180 V to 1.211 V.

Design a practical voltage divider

Solve for Vin, Vout, Rtop or Rbot, then compare standard resistor values, output limits and power. The worked examples below use exact nominal circuit values unless a tolerance is stated. The complete instructions and theory follow in expandable sections.

Worked example: unloaded and loaded output

With Vin = 5 V, upper resistor Rtop = 15 kΩ and lower resistor Rbot = 10 kΩ, the unloaded output is 5 × 10 / (15 + 10) = 2 V, measured at the resistor junction relative to return.

Unloaded output. Replaces current calculator inputs.

Adding Rload = 10 kΩ places it in parallel with Rbot = 10 kΩ. Call their equivalent resistance Re. Add the reciprocals of the two resistances, then take the reciprocal of that sum:

Re = 1 / (1/Rbot + 1/Rload)

Using resistance values in kΩ, Re = 1 / (1/10 + 1/10) = 1 / 0.2 = 5 kΩ. For two parallel resistors, this simplifies to Re = (Rbot × Rload) / (Rbot + Rload), so 10 × 10 / (10 + 10) gives the same result.

The loaded divider therefore has Rtop = 15 kΩ above an effective lower resistance Re = 5 kΩ. Its output becomes 5 V × 5 / (15 + 5) = 1.25 V.

Loaded output. Replaces current calculator inputs.

Worked example: resistor tolerance

Keep the unloaded supply at an exact 5 V and give each resistor ±1% tolerance. The minimum output uses Rtop = 15.15 kΩ and Rbot = 9.90 kΩ: 1.976 V. Rtop = 14.85 kΩ and Rbot = 10.10 kΩ give the maximum, 2.024 V. Supply and load limits can widen this range.

Resistor tolerance. Replaces current calculator inputs.

Worked example: dissipation is not the nameplate rating

In the exact unloaded example, Rtop drops 3 V and dissipates 3² / 15,000 = 0.6 mW. Rbot drops 2 V and dissipates 2² / 10,000 = 0.4 mW. A recommended nameplate wattage additionally accounts for worst-case limits, utilization and temperature derating; check the actual part’s datasheet.

Practical example: choose a standard resistor

Suppose a high-impedance input needs 1.200 V within ±3%, or 1.164–1.236 V, from a 3.300 V supply with ±1% variation. This acceptance band is the design requirement you compare with the results; it is not an additional calculator input.

  1. Select Solve for Rtop. Set Vin to 3.300 V and Target Vout to 1.200 V. Under Vin’s Limits, use symmetric percentage tolerance ±1%, giving 3.267–3.333 V.
  2. Set Rbot to 10.0 kΩ with ±1% tolerance, giving 9.90–10.10 kΩ. Keep Rload at No load. Select E96 and ±1% Tolerance for the solved resistor.

E96 standard-resistor selection. Replaces current calculator inputs.

The ideal upper resistance is 10 kΩ × (3.3 / 1.2 − 1) = 17.5 kΩ. Its adjacent E96 values are 17.4 kΩ and 17.8 kΩ. Open Compare nearby standard values to compare their complete output intervals:

E96 options with supply and both resistor tolerances included
RtopNominal VoutMinimum VoutMaximum VoutWorst target errorMeets ±3%?
17.4 kΩ1.204380 V1.177233 V1.231915 V2.6596%Yes
17.8 kΩ1.187050 V1.160173 V1.214317 V3.3189%No

Select 17.4 kΩ for this modeled requirement. Its ±1% resistance range is 17.226–17.574 kΩ, and its entire output interval fits the acceptance band. The 17.8 kΩ option falls below the allowed minimum, even though its nominal output fits. The recommendation minimizes worst-case target error among the bracketing standard values; it is specific to these inputs.

For the 17.4 kΩ option, maximum modeled dissipation is approximately 0.2601 mW in Rtop and 0.1503 mW in Rbot. At the default 50% utilization, 25 °C ambient, 70 °C full-rating and 125 °C zero-rating assumptions, the minimum nameplate powers are 0.5201 mW and 0.3005 mW. The smallest supported rating is 1/32 W for each resistor. This is a model-based wattage suggestion, not a checked physical part choice: verify availability, tolerance, voltage rating, temperature behavior and mounting conditions in the selected component’s datasheet.

How calculations are checked

Automated reference and regression checks compare loaded and unloaded outputs with expected divider results, and check that inverse calculations recover the requested voltage or resistance. Other checks cover standard-value selection, full tolerance bounds and current balance at the output node.

Power checks include cases where maximum dissipation occurs between resistance limits, plus utilization and temperature derating. Invalid and boundary inputs are checked for the expected rejection or limiting behavior. These checks verify the mathematical and software model; they are not physical bench measurements, certification or independent technical review.

To identify selected components, read axial resistor color bands or decode an SMD resistor marking. For several reference nodes, compare the multi-tap resistor ladder calculator.

How to use

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Quick start

  1. Under Solve for, choose Rtop, Rbot, Vin, or Vout.
  2. Under Ideal circuit, enter the other three values.
  3. Read the calculated value. Results update automatically.
  4. Check Resulting Vout range. When solving for Rtop or Rbot, this result uses the recommended standard resistor shown under Recommended standard Rtop or Recommended standard Rbot.

Only three circuit values are required. All other settings can be left at their defaults. The calculator automatically applies its default standard-resistor and tolerance settings. For an unloaded divider, leave Rload set to No load.

Use Reset to restore the default Solve for selection, circuit values, limits, load, standard-resistor settings, and power-rating settings. It also clears manually selected resistor recommendations, closes the comparisons, and recalculates all results.

Calculator features and benefits

Selecting practical voltage-divider components often requires repeated calculations: solve for the ideal resistance, try standard values, check tolerances, and calculate power. This calculator combines those steps and lets you compare alternatives as your design requirements change.

CapabilityHow it helps
Flexible solvingSolve for Rtop, Rbot, Vin, or Vout from the other three values. Switch the unknown without manually rearranging equations.
Automatic standard resistor recommendationWhen solving for Rtop or Rbot, automatically recommend a standard resistor for your Target Vout. Choose the E-series and resistor tolerance to match your design requirements.
Tolerance and worst-case analysisAccount for variations in Vin, Rtop, and Rbot. See minimum, nominal, and maximum Vout, along with percentage deviation from Target Vout when a target applies, to evaluate the complete output range.
Power dissipation and recommended ratingsCalculate maximum power dissipation in each divider resistor and automatically recommend standard power ratings with utilization margin and temperature derating.
Load effectsInclude Rload to evaluate how a load changes the output. When solving for Rtop or Rbot, the load is also included in the resistor calculation and standard-value recommendation.
Resistor comparisonsCompare nearby standard values or alternative Rtop/Rbot pairs without manually recalculating each option. Evaluate output accuracy, worst-case voltage range, current, and power to find the combination that best meets your requirements.

Advanced features

Enter circuit values and limitsShowHide

Under Ideal circuit, enter the known values for your divider:

  • Vin is the input voltage.
  • Vout is the voltage at the junction of Rtop and Rbot, measured relative to return. Target Vout is the desired output when solving for Rtop, Rbot, or Vin.
  • Rtop connects Vin to Vout.
  • Rbot connects Vout to return.

The value selected under Solve for is calculated automatically. To enter that value yourself, select a different unknown.

Check the resistance units: 1 kΩ = 1,000 Ω and 1 MΩ = 1,000,000 Ω.

Use the Limits row beneath an editable Vin, Rtop, or Rbot value to describe its allowed variation. You can enter:

  • A symmetric percentage, such as ±1%.
  • Separate negative and positive percentages.
  • An absolute tolerance.
  • Explicit minimum and maximum values.

For example, a 10 kΩ resistor with ±1% tolerance can range from 9.9 kΩ to 10.1 kΩ.

For the resistor being calculated, set its tolerance under Recommended standard Rtop or Recommended standard Rbot using Tolerance.

Review Resulting Vout range after changing limits to see their effect on the output.

Understand the recommended standard resistorShowHide

When solving for Rtop or Rbot, the calculator shows two resistance values:

  • Ideal Rtop or Ideal Rbot, under Ideal circuit, is the calculated resistance needed to meet Target Vout using the nominal circuit values.
  • Recommended value, under Recommended standard Rtop or Recommended standard Rbot, is the automatically recommended standard resistance.

The calculator defaults to All E-series and ±1% tolerance. Change E-series or Tolerance to match the components you intend to use.

E-series determines the available nominal resistance values. All E-series searches all preferred values in E24, E48, E96, and E192, with duplicates removed. Verify component availability and price with your distributor. Choosing E24, E48, E96, or E192 restricts the search to that series. Tolerance specifies how far the actual resistance may vary from its nominal value; it is a separate setting.

Open E-series reference below

Resulting Vout range uses the recommended standard resistance, or an alternative you have selected. This lets you see how a practical resistor affects the output compared with the ideal calculation.

The wattage beside Recommended value is the recommended power rating. Its calculation uses the settings under Resistor power ratings.

Read resulting Vout rangeShowHide

Resulting Vout range shows the output for the circuit values and limits being evaluated:

  • Min is the lowest calculated output within the entered limits.
  • Nominal is the output using nominal circuit values.
  • Max is the highest calculated output within the entered limits.

When a Target Vout applies, Deviation from target shows the percentage difference between each result and that target. Negative values are below target; positive values are above target.

The nominal deviation shows how closely the nominal circuit meets the target. The minimum and maximum deviations also account for the entered tolerances and limits. These deviations do not have to be symmetric.

The result depends on what you select under Solve for:

Solve forHow to interpret the output
Rtop or RbotThe ideal resistance meets Target Vout mathematically. The resulting output and range use the recommended standard resistor, or an alternative you have selected.
VinThe calculated ideal Vin produces Target Vout with the nominal resistor values. The output range shows the effect of resistor limits while holding Vin at that calculated value.
VoutThe output and its range are calculated from the entered Vin, resistor values, and limits.

Check that the entire Min-to-Max range meets your design requirements. These bounds cover the variations entered into the calculator, rather than every possible source of circuit error.

Include a load with RloadShowHide

Under Ideal circuit, use Rload to enter a resistance connected between Vout and return.

With the other circuit values held fixed, a finite load resistance lowers Vout. The calculator includes this loading effect in its results and shows the load on the schematic.

When solving for Rtop or Rbot, the calculator includes Rload when determining both the ideal resistance and the recommended standard value.

Review Resulting Vout range to check the loaded output. Set Rload back to No load to evaluate the unloaded divider.

See Theory & formulas for the loading equations and model limitations.

Compare nearby standard valuesShowHide

Open Compare nearby standard values under Recommended standard Rtop or Recommended standard Rbot.

This comparison evaluates nearby values for the resistor being calculated, using the selected E-series and tolerance. The other divider resistor remains fixed.

Compare each value’s nominal Vout and worst-case error. Choose Use to apply an alternative; Resulting Vout range and the power results then update for that value.

A value with slightly more nominal error may still be preferable because of another design requirement.

Use this comparison when you want to keep one resistor fixed and quickly evaluate alternatives for the other.

Compare Rtop / Rbot pairsShowHide

Open Compare Rtop / Rbot pairs to evaluate alternatives that change both divider resistors.

This gives you more choices than changing one resistor alone. Similar resistance ratios can produce similar nominal outputs while using different divider currents and power levels.

The comparison uses the selected E-series for both resistors and preserves each resistor’s current tolerance.

In general:

  • Higher resistance values reduce divider current and power, but make the output more sensitive to loading.
  • Lower resistance values increase divider current and power, but make the output less sensitive to loading.

Compare nominal accuracy, the complete output range, current, and power against your design requirements. You may also prefer a pair that uses resistor values already available in your design.

Choose Use pair to apply an alternative Rtop and Rbot to the calculator.

The closest nominal Vout is not always the best overall choice. Use the comparison results to decide which tradeoffs matter most for your circuit.

Understand and adjust resistor power ratingsShowHide

Open Resistor power ratings to review each divider resistor’s worst-case dissipation, recommended rating, and the assumptions used for the recommendation.

Voltage Divider evaluates Rtop and Rbot separately over the entered circuit limits. Adjust the maximum ambient temperature, utilization, and temperature-model settings when your operating conditions or selected resistor require different assumptions.

Open power-rating reference below
View detailed resultsShowHide

Open Detailed results to inspect additional calculated voltages, currents, and power values.

Use these results to check divider current, understand where power is dissipated, and investigate the effects of changing resistor values or adding a load.

See Theory & formulas for the equations and worked examples behind the calculations.

Back to calculator ↑

Theory & formulas

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Voltage divider formulas

A voltage divider uses two resistors to produce an output voltage that is a fraction of Vin.

  • Vin — input voltage: measured relative to Return.
  • Rtop — upper resistor: connects Vin to Vout.
  • Rbot — lower resistor: connects Vout to Return.
  • Vout — output voltage: measured at the junction of Rtop and Rbot, relative to Return.

With no load connected, the same current flows through both resistors. Equal resistors produce Vout = Vin/2. Increasing Rtop alone lowers Vout; increasing Rbot alone raises Vout.

These formulas assume Rload is set to No load.

Solve forFormula
VoutVout = Vin RbotRtop + Rbot
RtopRtop = Rbot (VinVout − 1)
RbotRbot = Rtop VoutVin − Vout
VinVin = Vout Rtop + RbotRbot

When solving for Rtop, Rbot, or Vin, Vout in these formulas means Target Vout.

Use consistent resistance units. For positive Vin and finite positive resistors, Vout must satisfy 0 < Vout < Vin.

Load effects — Rload

Rload represents a resistance connected between Vout and Return. It is in parallel with Rbot and lowers Vout for fixed Vin, Rtop, and Rbot.

Their combined resistance is:

Rlower = Rbot ∥ Rload = RbotRloadRbot + Rload

Rlower is the effective resistance of Rbot and Rload in parallel; it is not an additional resistor.

The loaded output is:

Vout = Vin RlowerRtop + Rlower

The calculator includes this loading effect when Rload is enabled. The unloaded formulas in the previous section do not apply directly to a loaded divider.

Resistance ratio and scale

Multiplying Rtop and Rbot by the same factor preserves the unloaded voltage ratio. With Vin fixed and no load, larger resistances reduce current and power.

For example, Rtop = 15 kΩ with Rbot = 10 kΩ and Rtop = 150 kΩ with Rbot = 100 kΩ both produce 2 V from an unloaded 5 V input. The second pair draws one-tenth the current.

With a fixed Rload, increasing both divider resistances makes loading more significant. The loaded output voltage does not remain unchanged.

Standard resistor values — E-series

Open E-series reference below

Ideal resistance and recommended standard value

Ideal Rtop or Ideal Rbot produces Target Vout using nominal circuit values. A standard resistor may be slightly above or below that ideal resistance.

When solving for a resistor, the calculator evaluates standard values around the ideal resistance using the selected E-series and tolerance. It recommends the candidate with the smallest worst-case absolute deviation from Target Vout. The closest resistance or closest nominal output is not necessarily the best choice across the full tolerance range.

Voltage, current, and power results use the recommended standard value, or the alternative standard value you select. Nominal Vout can therefore differ from Target Vout.

Vout range and deviation from target

  • Target Vout: the desired output voltage.
  • Nominal Vout: the output calculated from nominal circuit values, including the recommended or selected standard resistor when applicable.
  • Minimum/maximum Vout: the modeled output limits for the entered tolerances and limits.

For a nominal resistance R with symmetric fractional tolerance t:

Rmin = R(1 − t) Rmax = R(1 + t)

For ±1% tolerance, use t = 0.01. Other Limits settings define the lower and upper values directly or through the selected tolerance format.

The calculator evaluates combinations of the lower and upper limits for Vin and the resistors. When Rload is enabled, it uses the exact Rload value entered. Nominal results are calculated separately.

The reported range represents modeled worst-case bounds. It is not a statistical prediction of how likely a particular output voltage is.

Deviation from target

Deviation from target (%) = 100 × Vout − VtargetVtarget

Here, Vtarget means Target Vout. Positive deviation is above target; negative deviation is below target. This percentage requires a nonzero target.

Resistor power ratings

Power dissipation

A resistor’s power dissipation can be calculated from its own voltage drop and current:

P = VI = I2R = V2R

For the divider resistors:

Ptop = (Vin − Vout)2RtopPbot = Vout2Rbot

These formulas also apply with Rload enabled, using the loaded Vout. Calculate each resistor’s power separately because Rtop and Rbot carry different currents when a load is connected.

Worst-case power and rating selection

For each divider resistor, CircuitKitchen calculates Pmax over the entered Vin and resistor limits. It checks the tolerance-limit combinations and relevant intermediate resistance values that can produce an interior maximum-power condition.

CircuitKitchen then applies utilization margin and temperature derating when converting that calculated power into a recommended nameplate rating.

Open power-rating reference below

Assumptions and limitations

Results depend on the circuit values and limits entered.

  • Rload models a resistive load. Dynamic loading is not automatically included.
  • Temperature coefficient, long-term drift, and wiring resistance are not automatically included.

The power-rating reference includes the rating model and its datasheet limitations.

Back to calculator ↑

E-series resistor values

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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

SeriesValues per decadeSignificant digitsCommonly associated tolerances
E332No tolerance association listed in the cited Vishay table
E662±20%
E12122±10%
E24242±5%
E48483±2%
E96963±1%
E1921923±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.

Rmin = Rnominal × (1 − t) Rmax = Rnominal × (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

  1. Define the circuit requirements. Establish the desired resistance or circuit output, acceptable error, operating conditions, and relevant size, voltage, and power constraints.
  2. Calculate the ideal value. Determine the resistance that would produce the desired result with ideal components.
  3. 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.
  4. 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.
  5. 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.
  6. 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.
  7. 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 101/N.

Ideal step = 100 × (101/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
  • 1.0
  • 2.2
  • 4.7
E6 — 6 values per decade
  • 1.0
  • 1.5
  • 2.2
  • 3.3
  • 4.7
  • 6.8
E12 — 12 values per decade
  • 1.0
  • 1.2
  • 1.5
  • 1.8
  • 2.2
  • 2.7
  • 3.3
  • 3.9
  • 4.7
  • 5.6
  • 6.8
  • 8.2
E24 — 24 values per decade
  • 1.0
  • 1.1
  • 1.2
  • 1.3
  • 1.5
  • 1.6
  • 1.8
  • 2.0
  • 2.2
  • 2.4
  • 2.7
  • 3.0
  • 3.3
  • 3.6
  • 3.9
  • 4.3
  • 4.7
  • 5.1
  • 5.6
  • 6.2
  • 6.8
  • 7.5
  • 8.2
  • 9.1
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

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 = VR × I = I² × R = VR² / R, where VR 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, Pbasis is that resistor's maximum modeled continuous dissipation, Pmax. 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, Pi = Iladder² × Ri. 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, Pi = V² / Ri, 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 Ifmax with an unrelated Rmax 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:

Ta
highest expected local ambient temperature near the resistor.
Tref
temperature through which the model allows full rated power.
Tzero
temperature at which the model allows zero power.
kt
available fraction of nameplate power.

Tzero must exceed Tref. Use finite, valid settings. When dissipation is positive and kt = 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. Ta 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: ku = Ku_percent / 100. A 50% setting means ku = 0.50. Similarly, a displayed Kt of 100% means kt = 1.00; some panels display Kt directly as a fraction.

These equations apply with positive valid ku and kt. 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 Prated,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 Ta = 25 °C, Ku = 50%, Tref = 70 °C, and Tzero = 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, kt = 1.00 and ku = 0.50. For Pbasis = 100 mW:

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

At Ta = 85 °C with the same Tref, Tzero, 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, Ppeak,worst = 1 W and D = 0.10 give Pbasis = 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 = Ppeak × ton 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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