Ohm's Law Calculator
Calculate Voltage, Current, Resistance, and Power instantly by entering any two known values.
Runs in your browser Your input never leaves your device.
About this tool
Fill in any two of voltage (V), current (A), resistance (ohms) and power (W), and the calculator solves for the other two. It uses V = I x R and P = V x I, plus the derived forms such as P = V^2 / R and P = I^2 x R. Values are in base units, so enter 0.02 for 20 mA or 4700 for 4.7 kilohms. Results are rounded to three decimal places. If you fill in more than two fields it uses one pair, checked in the order V and I, V and R, V and P, I and R, I and P, then R and P, and ignores the rest without checking they agree. It assumes a simple resistive DC circuit.
How to use it
- Fill in any two of the four fields.
- Leave the other two empty.
- Read all four values in the results.
Example
I = 12 / 6 = 2 A and P = 12 x 2 = 24 W.
Voltage 12 V, Resistance 6 ohms
Voltage: 12 V Current: 2 A Resistance: 6 Ω Power: 24 W
Common problems
- The result says 'Enter any two values'
- At least two fields must have numbers. Clear the others so they are empty.
- Three or more fields are filled and the answer looks wrong
- Only one pair is used and the rest are ignored. Clear all but two fields.
- Very small values show as 0
- Results are rounded to three decimals. Use larger base units, for example work in amps rather than microamps.
- Results show Infinity or NaN
- Dividing by zero current, resistance or voltage is not meaningful.