The formulas
DC: A = W ÷ V
AC single-phase: A = W ÷ (V × PF)
AC three-phase: A = W ÷ (√3 × V × PF)
Examples
- A 1,000 W load at 12 V DC draws 83.3 A, but only 4.3 A at 230 V and 8.3 A at 120 V.
- A 60 W 12 V fridge draws 5 A when running.
- A 2,000 W motor on 230 V with a power factor of 0.8 draws 10.9 A.
The big difference between 12 V and mains current is why 12 V wiring needs much thicker cable for the same power.
Frequently asked questions
How many amps is 1000 watts at 12V?
About 83 A. Through an inverter, add around 12% for losses, so roughly 95 A from the battery.
How many amps is 3000 watts at 230V?
About 13 A, which is the maximum for a UK plug. At 120 V it's 25 A.