Electronics CalculatorsVoltage divider calculator
Enter the input voltage and the two resistors. Add a load resistance to see how much it pulls the output down.
The formula
For two resistors in series across a voltage, the output taken across R2 is Vout = Vin × R2 / (R1 + R2).
The target feature
Give R1, the input and the output you want, and leave R2 empty. The tool gives R2 = R1 × Vout / (Vin − Vout) and the nearest E24 value.
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A divider works only if whatever you connect to the output draws very little current. If it draws a lot, the load is in parallel with R2 and lowers the output. The page on divider limits has a worked example.
How it was tested
300 random dividers were compared with direct calculation, with and without a load, and the loaded output was always lower than the unloaded one.
Can I use a divider to power something?
Only a tiny load. For power, use a regulator.
What values should I choose?
A current of a fraction of a milliampere through the divider is typical for signals. Lower resistor values waste more power.
This is an independent guide. It is not connected with any standards body or company named here. The formulas are the usual textbook ones; the colour code, E-series and AWG values are those printed in common references, because the standards IEC 60062, IEC 60063 and ASTM B258 are paid documents that we did not read. Tables and examples were calculated with Python on 14 November 2026. Check data sheets and local safety rules before you build.