Find current I = V / R and the power P = V I dissipated in a resistor.
| Current (A) | – |
| Power (W) | – |
Use this calculator for a DC resistor: current is voltage divided by resistance, and the power turned into heat is V I (also I² R or V² / R).
A 12 V supply on 4 Ω draws 3 A and dissipates 36 W. Real parts have tolerance and temperature drift. This is DC only; AC with phase and reactance is a different circuit. Resistance must be greater than zero.
Voltage (V): Potential difference across the resistor, in volts.
Resistance (Ω): Resistance in ohms, not zero.
Current (A): I = V / R, in amperes.
Power (W): P = V I, in watts.
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