Ohm’s Law Calculator

Ohm’s law states that the voltage across a resistor equals the current through it times its resistance: V = IR. It only applies to ohmic materials, where current is proportional to voltage.

Rearrange V = IR to R = V / I. Divide the voltage across the resistor by the current through it. A 12 V battery pushing 2 A through a bulb means the bulb’s resistance is 6 Ω.

Electric power is P = VI: multiply voltage by current. A 12 V device drawing 2 A consumes 24 W. You can also write it as P = I²R or P = V²/R.

Voltage in volts (V), current in amperes (A), resistance in ohms (Ω), and power in watts (W). Common prefixes apply: a 4.7 kΩ resistor is 4,700 Ω, and 20 mA is 0.02 A.

Only as a sign convention for direction — the magnitude is what the formulas use. This calculator works with magnitudes, so it asks for non-negative values.