Electronics & Engineering

Voltage Divider Calculator

Find the output of a resistor divider from the input voltage and R1 and R2.

By TheCalcTools Updated Formula checked and tested

Your numbers

Your results

Output voltage (V)
Output voltage (V)
—
Current (mA)
—
Total power (mW)
—
Division ratio
—

Voltage Divider Calculator by TheCalcTools

How the Voltage Divider Calculator works

Enter the supply voltage and the two resistor values. R2 is the resistor the output is measured across.

The same current flows through both resistors.

The output is the supply times R2 over the total resistance.

The formula

Vout = Vin × R2 ÷ (R1 + R2)I = Vin ÷ (R1 + R2)

Worked example

Using the default values shown in the calculator:

Input voltage (V)12
R1 (Ω)10000
R2 (Ω)5000
  1. Vout = 12 × 5,000 ÷ 15,000 = 4.00 V.
  2. Current = 12 ÷ 15,000 = 0.80 mA.
  3. Power = 9.60 mW.

Result:

Output voltage (V)4.0000
Current (mA)0.8000
Total power (mW)9.600
Division ratio0.3333

Frequently asked questions

Does a load change the output?

Yes. A load in parallel with R2 lowers the output. The load resistance should be much larger than R2 (ideally 10× or more) for the formula to hold.

Can I use a divider to power a device?

Not usually. Dividers waste power and the output sags under load. Use a regulator instead.

Sources and further reading

Ohm's Law CalculatorPick the two values you know and get the other two Resistors in Series and Parallel CalculatorCombine up to four resistors LED Resistor CalculatorPick a resistor that sets the right current through an LED Electrical Power Calculator (Single and Three Phase)Work out watts, kVA and kvar from volts, amps and power factor Capacitors in Series and Parallel CalculatorCombine up to four capacitors Resistor Color Code CalculatorChoose the colours of the four bands to read the value

More in Electronics & Engineering · All calculators

This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.