Voltage Divider Calculator

Output voltage, current and the power each resistor dissipates.

Output voltage, current and the power each resistor dissipates. Vout = Vin × R2 ÷ (R1 + R2).

Written and maintained by Mohit PatelLast checked August 4, 2026How we build these

Input voltage

R1 (upper)

R2 (lower)

This assumes nothing is drawing current from the output. Connecting a load places it in parallel with R2, which lowers the output voltage — often substantially. A divider is fine for a reference into a high-impedance input and unsuitable as a power supply.

Output voltage (V)

4 mA through the divider

Output voltage8 V

Divider ratio0.66667

Current4 mA

Power in R116 mW

Power in R232 mW

Total power48 mW

Vout = Vin × R2 ÷ (R1 + R2). The ratio is all that sets the output, so 1k/2k and 10k/20k both give 8 V — but the larger pair wastes ten times less current. The catch is that a divider is only accurate unloaded: anything drawing current from the output sits in parallel with R2 and pulls the voltage down.

How the Voltage Divider Calculator works

Vout = Vin × R2 ÷ (R1 + R2). The ratio alone sets the output, so 1k/2k and 10k/20k give the same voltage, but the larger pair wastes ten times less current. The catch is that a divider is only accurate unloaded.

Also known as: voltage divider formula · resistor divider calculator · potential divider calculator · vout calculator

Where to go next

The Voltage Divider question rarely arrives on its own. These are the ones that usually come with it:

Resistor Calculator — Series and parallel totals for up to four resistors.
LED Resistor Calculator — The series resistor, rounded up to a standard value.
Speed Distance Time Calculator — Any one of the three from the other two, in four units.
Acceleration Calculator — Acceleration in m/s² and in g, which is the legible one.

Sources

Frequently asked questions

What is the voltage divider formula?

Vout = Vin × R2 ÷ (R1 + R2). With 12 V across 1 kΩ and 2 kΩ, the output is 8 V.

Why does my divider output drop under load?

Because the load sits in parallel with R2, lowering the effective resistance and the output voltage. A divider is fine feeding a high-impedance input and unsuitable as a power supply.

Which resistor values should I choose?

The ratio sets the voltage; the absolute values set the current wasted. Larger values waste less power but are more affected by any load and by noise.

How much power do the resistors dissipate?

Current squared times resistance, for each. This page shows both, which is what determines the rating you need.

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