Ohm's law calculator — volts, amps, ohms and watts

How it works: Ohm's law calculator

Ohm's law V = I × R says voltage equals current times resistance, and power P = V × I. Enter any two known values to get the rest — a 3,500 W water heater on 220 V draws about 15.9 A, so a 20 A breaker suits it.

Results hold for DC and resistive AC loads; motors have a power factor that makes the real current a little higher. Have household wiring checked by a licensed electrician.