Ohm's Law Calculator
V = I × R. Fill in any two of voltage, current and resistance; leave one empty and get it.
Example — 12 volts across 4 ohmsI = 3 amps
Leave exactly one box empty — that is the one to solve for.
How we got it — the example, step by step
- Ohm's law turned around: I = V ÷ R.
- = 12 ÷ 4 = 3 A.
Check it backwards
3 × 4 = 12 V — the voltage we started with.
Questions people also ask
What are the units?
Volts (V), amps (A) and ohms (Ω). The three are defined so that 1 volt across 1 ohm pushes exactly 1 amp.