Ohm's Law Calculator

Enter any two of voltage, current, resistance or power, and get the other two worked out instantly.

Known values
All four values
Voltage V
Current A
Resistance Ω
Power W
Enter any two values — the other two are worked out as you type.

Every calculation happens in your browser — the numbers you type never leave your device.

FAQ

Which values do I enter?

Fill in any two of voltage, current, resistance or power and leave the rest blank. The other two are calculated for you, and all four are shown together so you can copy any of them.

How is power calculated?

Power comes from the pair you enter: voltage times current, current squared times resistance, or voltage squared divided by resistance — all three give the same watts for a simple resistive circuit.

Do I need to convert units first?

Yes — enter volts, amperes, ohms and watts directly. If you have milliamps or kilohms, convert them to the base unit first, for example 250 mA is 0.25 A and 4.7 kΩ is 4700 Ω.

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