Watts Volts Amps Calculator
Electrical power is how fast a device uses energy, measured in watts. It comes from the voltage across a device and the current through it. This page works out watts from any pair of volts, amps and ohms you know.
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How it works
Power equals volts times amps. If you know volts and resistance instead, power is volts squared divided by ohms. If you know amps and resistance, power is amps squared times ohms. These are three forms of the same law.
The result is the power a device uses under those conditions. It does not say how a circuit should be wired or protected, which is a job for the wiring rules.
Worked example
At 120 volts and 15 amps, the power comes to 1,800 W.
Questions
Is a watt the same as a watt-hour?
No. A watt is a rate of using energy, and a watt-hour is the energy used over one hour at that rate.
Where do I find the volts and amps of a device?
The label or manual usually lists the voltage and the power. If you know the power and voltage, dividing one by the other gives the amps.
Does this give the power a circuit can supply?
No. It finds the power a device draws from the values you enter. Circuit limits come from the wiring and its protection, not from this page.
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