How to Convert Watts to Amps
Watts measure real electrical power, amps measure current, and volts measure electrical pressure. The three are linked by Watt's law, P = V × I, so current is always power divided by voltage: I = P ÷ V. That relationship is exact for DC circuits. For AC circuits, voltage and current can be out of phase, so the calculation also needs the power factor (PF) — and for three-phase AC, a √3 factor that accounts for the three-wire geometry of the supply.
The formula for each circuit type
This calculator uses three standard forms of the same underlying relationship, selected by the Circuit Type field:
- DC: I = P ÷ V — power factor does not apply to direct current.
- AC, single phase: I = P ÷ (PF × V) — used for standard 120 V/230 V household and single-phase equipment circuits.
- AC, three phase (line-to-line voltage): I = P ÷ (√3 × PF × V) — used for three-phase motors, HVAC equipment, and industrial supplies, where √3 ≈ 1.732 and V is the voltage measured between any two of the three lines.
Understanding power factor
In an AC circuit, real power (watts, what you pay for and what does useful work) equals apparent power (volt-amps) times the power factor: P = S × PF, or equivalently P = V × I × PF. Power factor ranges from 0 to 1 and reflects the phase difference between voltage and current caused by inductive loads like motors, transformers, and fluorescent ballasts. Purely resistive loads — incandescent bulbs, resistive heaters, and DC circuits — have a power factor of 1.0, meaning voltage and current stay perfectly in step. A lower power factor means more current is required to deliver the same real power, which is why motor and HVAC nameplates typically list a power factor between 0.8 and 0.95.
Sizing wiring and breakers from the result
The current this calculator returns is the steady-state operating current for the load as described. When sizing wire gauge or a circuit breaker, electricians typically apply a safety margin (commonly 125% of the continuous load current per NEC guidance) rather than wiring to the exact calculated amperage — always verify against your local electrical code and, for anything beyond a simple household outlet calculation, consult a licensed electrician.