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Voltage Divider Calculator

Enter the input voltage and both resistor values to find the output voltage across R2.

Formula

  • Vout = Vin × R2/(R1+R2)

Vin is the input voltage, R1 and R2 are the divider's two resistors, and Vout is the voltage measured across R2.

About this calculation

A voltage divider is two resistors in series across an input voltage. The current through both is the same, so the input divides in proportion to the resistances, and the output taken across R2 is Vout = Vin × R2 / (R1 + R2). It is the usual way to scale a signal down to an ADC input or to set a reference level.

Assumptions and limits

  • The output is assumed unloaded. Anything that draws current from the output sits in parallel with R2 and pulls the voltage down.
  • Both resistors are ideal and constant; the divider drawn current and resistor tolerance are not modelled.
  • For AC signals the ratio holds while the divider is resistive and the load impedance is much higher than R1 and R2.

A worked example

With 12 V across R1 = 1 kΩ and R2 = 1 kΩ, the output is 12 × 1000 / (1000 + 1000) = 6 V — the input split evenly because the two resistors are equal.

See also Current Divider and ADC Resolution.