Ohm's Law Calculator

Ohm's law links voltage, current and resistance (V = I × R), and the power law adds power (P = V × I). Knowing any two of the four values is enough to find the other two. Fill in the two you know and the calculator does the rest, showing which formulas it used.

How to use Ohm's Law Calculator

1. Enter any two values: voltage in volts, current in amps, resistance in ohms or power in watts.
2. Leave the other two empty.
3. Read the calculated values and the formulas.

When it comes in handy

• Choosing a resistor for an LED or sensor.
• Checking the current a heater or motor draws.
• Electronics and physics homework.

Frequently asked questions

Which formulas are used?

V = I × R, I = V ÷ R, R = V ÷ I, P = V × I, P = I² × R and P = V² ÷ R, depending on which two values you enter.

Does it work for AC circuits?

For purely resistive AC loads, using RMS values, yes. Circuits with capacitors, inductors or motors also have reactance and a power factor, which this simple calculator does not include.