Voltage Divider Calculator

Work out the output of a two-resistor voltage divider, or choose the resistor that gives the voltage you need.

Circuit: Vin → R1 → Vout → R2 → ground (0 V).

The voltage divider formula

A voltage divider (also called a potential divider) is two resistors in series across a supply. The output is taken from the point between them. Because the same current flows through both resistors, the supply voltage is shared in proportion to their resistances: Vout = Vin × R2 ÷ (R1 + R2).

Worked example

With Vin = 12 V, R1 = 10 kΩ and R2 = 4.7 kΩ, the output is 12 × 4,700 ÷ 14,700 = 3.84 V. The current through both resistors is 12 ÷ 14,700 = 0.816 mA, so each resistor dissipates well under a milliwatt.

To get 5 V from 12 V with R1 = 10 kΩ, rearrange the formula: R2 = Vout × R1 ÷ (Vin − Vout) = 5 × 10,000 ÷ 7 = 7.14 kΩ. The nearest E24 resistor is 7.5 kΩ, which gives 5.14 V.

Where voltage dividers are used

• Scaling a battery or sensor voltage down for a microcontroller's analogue input.
• Setting the bias voltage of a transistor amplifier.
• Reading light-dependent resistors and thermistors, which form one half of the divider.
• Setting the output voltage of adjustable regulators such as the LM317.

A potentiometer is a voltage divider in a single part: its wiper splits the track into R1 and R2.

Frequently Asked Questions

Related tools: Ohm's Law Calculator and Series and Parallel Calculator.