How to Convert Amps to Watts
Amps tell you how much current flows through a conductor; watts tell you the total power consumed. Converting amps to watts is essential for sizing generators, inverters, UPS backups, and shore-power connections - where the equipment is rated in watts but circuits and breakers are rated in amps.
DC Power Formula
For direct-current systems, power equals voltage times current:
PW=V×I
A 30 A charge controller at 12 V delivers 360 W. A 20 A trolling motor at 24 V draws 480 W. DC calculations are the basis for solar, battery, and automotive design.
AC Single-Phase Formula
PW=V×I×PF
AC Three-Phase Formula
PW=√3×VL-L×I×PF
Use line-to-line voltage (208 V, 480 V) for three-phase calculations, not line-to-neutral. The 1.732 factor accounts for the phase offset between the three conductors.
Apparent Power vs Real Power
Watts (W) are real power - actual work done. Volt-amps (VA) are apparent power - what the utility meter sees. The ratio VA to W is 1/PF. Generators and UPS backups are rated in VA because that is the current they must supply regardless of the load's power factor.Quick Conversion Reference
| Amps | at 120 V | at 240 V | at 12 V DC |
|---|---|---|---|
| 1 A | 120 W | 240 W | 12 W |
| 5 A | 600 W | 1200 W | 60 W |
| 15 A | 1800 W | 3600 W | 180 W |
| 20 A | 2400 W | 4800 W | 240 W |
| 30 A | 3600 W | 7200 W | 360 W |
Breaker Continuous-Load Limit
A 20 A breaker on a 120 V circuit handles 2400 W momentarily, but only 1920 W continuously (80% rule). Loads running 3 hours or more - like heaters, EV chargers, or lighting circuits - must fit under the continuous limit.