Watts, Volts & Amps Calculator
The everyday DC power conversion, made instant. Enter any two of watts, volts, and amps, and get the third — plus all three shown together so you can size a supply, a fuse, or a wire with confidence.
For DC systems, power is simply volts × amps. AC with a power factor is not covered here.
Formula & how it works
The relationship is P = V × I. Rearranged, I = P ÷ V and V = P ÷ I. Enter any two and the third follows.
Worked example
Twelve volts at 2 amps is 12 × 2 = 24 watts. Working the other way, a 60 watt load on 12 volts pulls 60 ÷ 12 = 5 amps, and a 100 watt load at 5 amps implies a 20 volt supply.
Sizing DC systems
Watts describe the job, amps stress the wires
Power in watts tells you how much work a load does, but it is the current in amps that heats conductors and trips fuses. That is why the same 60 watts is easy at 12 volts (5 amps) but trivial at 120 volts and punishing at 5 volts (12 amps) — lower voltage means more current for the same power.
Pick the supply, then check the current
When choosing a power supply, add up the watts your loads need and confirm the supply can deliver them at your system voltage. Then check the resulting amps against your wiring and connectors, because a supply rated for the wattage still overheats thin wire if the current is too high for it.
DC only here
This simple product holds for direct current. On alternating current, some of the volt-amps do no real work, captured by the power factor, so watts come out lower than volts times amps. For battery, solar, and USB projects, though, the straightforward DC relationship is exactly what you want.