Ohm’s Law Calculator

Ohm’s law states that the voltage across a resistor equals the current through it times its resistance: V = I × R. Rearranged, it also gives I = V ÷ R and R = V ÷ I. It is the fundamental relationship linking voltage, current, and resistance in an electrical circuit.

Power is voltage times current: P = V × I, measured in watts. Using Ohm’s law you can also write it as P = I² × R or P = V² ÷ R. This calculator gives you the power automatically once you enter any two of voltage, current, resistance, or power.

Voltage (V) is measured in volts and is the electrical "pressure." Current (I) is measured in amperes (amps) and is the rate of charge flow. Resistance (R) is measured in ohms (Ω) and opposes current. Power (P) is measured in watts and is the rate of energy use.

Exactly two. Ohm’s law and the power equation let you derive the other two from any pair. Enter, for example, voltage and resistance, and the calculator finds the current and power. Leave the two unknown fields blank.

A 12-volt car circuit with a 4-ohm resistor draws I = V ÷ R = 12 ÷ 4 = 3 amps, and dissipates P = V × I = 12 × 3 = 36 watts. Ohm’s law is used constantly in electronics to choose resistors, size wires, and stay within power limits.