Voltage Divider Calculator

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This tool calculates the voltage drop across each resistor in a series network of two resistors.

Enter

  • Input Voltage Vin
  • R1 and R2 in milliOhm/Ohm/kiloOhm/megaOhm

Formula

Ohm’s law is used to calculate the voltage drops. The current through each series resistor is the same as the total current through the circuit.

Therefore the total current Itotal is given by

Itotal = Vin/(R1+R2) = V1/R1

V1=Vin*R1/(R1+R2)

Itotal = Vin/(R1+R2) = V2/R2

V2=Vin*R2/(R1+R2)

The largest voltage drop will be across the larger resistor value. Conversely, the smallest voltage drop will be across the smaller.

If you want to calculate the voltage drop across a single resistor set R2=0 and from the equations above, V1=Vin and V2=0 (which makes sense).

Example Calculation

With R1=1Ω, R2=3Ω, Vin=12V, the voltages

  • V1=3V
  • V2=9V

The sum of the two voltages = the input voltage. As a check you can see that 3+9= 12V

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