The formulas
DC: W = A × V
AC single-phase: W = A × V × PF
AC three-phase: W = √3 × A × V × PF
Examples
- A 12 V appliance drawing 5 A uses 60 W.
- A 13 A UK socket at 230 V can supply up to 2,990 W.
- A 15 A US circuit at 120 V supplies up to 1,800 W, with continuous loads normally kept to 80% (1,440 W).
Frequently asked questions
How many watts is 10 amps at 12V?
120 W.
How many watts can a 13 amp plug take?
About 3,000 W at 230 V (13 × 230 = 2,990 W).