Voltage Divider Calculator
Output voltage, current and the power each resistor dissipates.
Work out Voltage Divider. Output voltage, current and the power each resistor dissipates. Free, with no account and nothing to download.
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)
8
4 mA through the divider
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
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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