Enter two of voltage, current and resistance to find the third and the power, using Ohm's law (V = I × R).
Last updated: November 8, 2026
How voltage, current and resistance relate
Ohm's law says the current through a conductor is proportional to the voltage across it and inversely proportional to its resistance: • V = I × R (voltage = current × resistance) • I = V ÷ R • R = V ÷ I • Power: P = V × I = I² × R = V² ÷ R Example: 2 A flowing through a 6 Ω resistor needs 2 × 6 = 12 V, and the resistor dissipates 12 × 2 = 24 W. The law holds for linear (ohmic) parts such as resistors. In diodes, LEDs and bulbs the resistance changes with current and temperature.
Common questions about Ohm's law
V = I × R, with voltage in volts, current in amperes and resistance in ohms. Knowing any two gives you the third.
Other tools you may find useful
In amperes.
In ohms.