Ohm's Law Calculator (V = IR)
Fill in any two of voltage (V), current (I) and resistance (R). Leave the third blank and press calculate. Power is calculated too.
Ohm's law formulas
- V = I × R (voltage = current × resistance)
- I = V ÷ R
- R = V ÷ I
- Power: P = V × I = I²R = V² ÷ R (in watts)
Worked examples
Find current: a 12 V battery across a 4 Ω resistor. I = 12 ÷ 4 = 3 A, and P = 12 × 3 = 36 W.
Find resistance: 230 V and 2 A. R = 230 ÷ 2 = 115 Ω.
Find voltage: 0.5 A through 100 Ω. V = 0.5 × 100 = 50 V.
Ohm's law holds for ohmic conductors at constant temperature. Devices like diodes and filament bulbs do not follow it. Find more electrical formulas in the Formula Library of the full Calvo calculator.
FAQ
What is Ohm's law?
Ohm's law states that the current through a conductor is directly proportional to the voltage across it, so V = IR.
What unit is resistance measured in?
Resistance is measured in ohms (Ω), current in amperes (A) and voltage in volts (V).
How do I calculate electrical power?
Use P = V × I, or equivalently P = I²R or P = V²/R. The result is in watts.
Does Ohm's law work for all components?
No. It applies to ohmic conductors such as metal wires and resistors at constant temperature.