Ohm’s Law Calculator
Find voltage, current, resistance and power from any two of them.
The core law of circuits
Ohm’s law says voltage equals current times resistance: V = I × R. Power is voltage times current: P = V × I. Knowing any two of the four values lets you work out the other two.
Example
On the first tab (voltage and current) with the starting values shown (Voltage 12 V; Current 2 A), Resistance comes out as 6. Other results include power: 24.
These formulas apply to simple resistive circuits with direct current, and also to alternating current with resistive loads. Circuits with coils or capacitors need more care. Working with mains electricity is dangerous, so use a qualified electrician.
Frequently asked questions
What are the units?
Volts for voltage, amperes (amps) for current, ohms for resistance and watts for power.
What is the Ohm's law triangle?
A memory aid: cover the value you want, and the other two show how to calculate it.
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