Ohm's Law Calculator

Enter any two of voltage, current, resistance, and power; the other two are solved instantly. V = I × R and P = V × I. Runs locally in your browser.

Enter any two values. Type the unit with SI prefixes — e.g. 5V, 20mA, 4.7kΩ, 2.2MΩ, 10mW. The two you fill in are inputs; the rest are computed.

Voltage

volts (V), e.g. 12V, 3.3V

Current

amps (A), e.g. 2A, 20mA, 500µA

Resistance

ohms (Ω), e.g. 220Ω, 4.7kΩ, 1MΩ

Power

watts (W), e.g. 0.25W, 100mW

Enter any two known values and the calculator solves the other two using V = I × R and the power equation P = V × I = I² × R = V² ÷ R. Type a unit with an SI prefix to parse it: m (milli, 10⁻³), k (kilo, 10³), M (mega, 10⁶), and µ (micro, 10⁻⁶) for current. A blank or zero-derived field means the value can't be determined from your two inputs (for example, R is undefined when both V and I are zero). Runs locally — nothing leaves your browser.