Ohm's Law Calculator
Voltage, current, and resistance are tied together by V = IR. Enter any two and it fills in the rest, power included.
Type any two of voltage, current, and resistance. The calculator fills in the missing one and works out the power along the way.
Voltage
12V
Current
2A
Resistance
6Ω
Power
24W
How it works
Ohm's law links three quantities: voltage equals current times resistance, or V = IR. Push 2 amps through 6 ohms and you need 12 volts to do it.
Any two of the three lock in the last one. Leave a field blank and the tool rearranges: current is voltage over resistance, resistance is voltage over current. It skips a divide-by-zero rather than showing a garbage number.
Power comes along for free. Multiply voltage by current and you get watts — how fast the component turns electrical energy into heat or light. That 12 V at 2 A works out to 24 watts.
Frequently asked questions
What is Ohm's law?
A simple rule that voltage across a resistor equals the current through it times its resistance, V = IR. It's the backbone of nearly every basic circuit calculation.
How do I calculate power from Ohm's law?
Multiply voltage by current: P = V·I. With 12 volts and 2 amps you get 24 watts. The calculator shows this automatically once it has enough to know both values.
Which two values should I enter?
Whichever two you actually know. Measured the voltage and resistance? Enter those and read off the current. Any pairing works, and the third field plus the power update instantly.