Ohm's Law Calculator
Choose which value to solve for, enter the other two, and get the result plus power in watts.
How Ohm's law works
Ohm's law relates voltage (V, in volts), current (I, in amps), and resistance (R, in ohms) with the formula V = I × R. Rearranged, that also gives I = V / R and R = V / I.
Electrical power (P, in watts) is calculated as P = V × I — the rate at which electrical energy is converted in the circuit. Combining it with Ohm's law also gives P = I²R and P = V²/R.
Frequently asked questions
What is Ohm's law?
Ohm's law states that the voltage across a conductor is directly proportional to the current flowing through it, with resistance as the constant of proportionality: V = I × R.
How do I calculate power from voltage and current?
Multiply voltage by current: P = V × I. For example, 12 V at 2 A gives 24 W of power.
What units does this calculator use?
Voltage in volts (V), current in amps (A), resistance in ohms (Ω), and power in watts (W) — the standard SI units for basic circuit analysis.