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Calculator · Electrical · SI unit · James Watt 1882

Watts

Units of watts and the conversions every electrical engineer needs in one place. The watt is the SI unit of power — one joule per second. The calculator below derives watts from voltage and current (or any combination of V·I·P·R) and converts to kilowatts, horsepower, BTU/hour, and kcal/hour automatically. Includes the watts × volts product, kVA in watts conversion, and watts to amps calculation for both 120 V and 240 V circuits.

W V I power formula W = V x I watts (power) volts amps Common ratings appliance W V A LED bulb 10 120 0.08 60 W bulb 60 120 0.5 Laptop 65 120 0.55 Microwave 1100 120 9.2 AC unit 1500 120 12.5 Electric range 5000 240 20.8 EV charger L2 7700 240 32 DC: P = V x I • AC 1ph: P = V x I x cos(phi)
Figure 1 — Power triangle W = V x I, with common appliance ratings (US 120/240 V mains)