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Watts, amps & volts calculator

Know two of watts, amps, volts or ohms? Get the rest, with Ohm’s law worked out step by step.

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Power 1,800 W

How it works

W = V × A · V = A × Ω

Two short formulas cover it. Power is voltage times current (W = V × A), and voltage is current times resistance (V = A × Ω, Ohm’s law). Know any two of the four and you can find the other two. For a household circuit: 120 V × 15 A = 1,800 W, which is why a 1,500 W space heater and a 1,200 W microwave on the same circuit trip the breaker.

  1. Power = volts × amps 120 V × 15 A = 1,800 W
  2. Resistance = volts ÷ amps 120 V ÷ 15 A = 8 Ω

Good to know

  • For AC appliances these formulas give the real power only when the load is purely resistive (heaters, kettles, incandescent bulbs). Motors and power supplies draw a little more current than watts ÷ volts suggests.

Printed from rocketcalc.io/tech/ohms-law