Ohm's Law Calculator - Solve for Voltage, Current, Resistance, or Power

Ohm's Law states that the voltage (V) across a conductor is directly proportional to the current (I) flowing through it, with resistance (R) as the constant of proportionality. The core formula is V = I × R.

Power (W) can be derived from Ohm's Law using three equivalent formulas: P = V × I, P = I² × R, or P = V² / R. This calculator automatically applies the correct formula based on your two known values.

This tool uses standard SI units: Volts (V) for voltage, Amperes (A) for current, Ohms (Ω) for resistance, and Watts (W) for power.

Ohm's Law applies directly to DC circuits and purely resistive AC circuits. For reactive AC circuits with capacitors or inductors, impedance (Z) replaces R. For those cases, the relationship becomes V = I × Z.

Resistance (Ω) is the opposition to current in both AC and DC circuits due to material properties. Impedance (Z) is the total opposition in AC circuits, combining resistance with reactance from capacitors and inductors. For purely resistive circuits, impedance equals resistance.

This calculator uses standard IEEE 754 double-precision floating-point arithmetic, providing results accurate to 4–6 significant figures for typical engineering values. For precision metrology, always calibrate with physical measurements.

One Ohm (1 Ω) is the resistance that allows exactly 1 Ampere of current to flow when 1 Volt is applied. It is the base SI unit of electrical resistance, named after German physicist Georg Simon Ohm.

All Ohm's Law calculations are performed locally in your browser using JavaScript. No electrical values, formulas, or inputs are ever transmitted to any server, ensuring complete privacy for your engineering work.