Amps to Watts Calculator
Watts show how much power a circuit delivers. For direct current, watts are amps times volts. Alternating current adds a power factor, and three phase adds a square root of three.
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How it works
For DC, power in watts is amps times volts. For single phase AC, multiply that by the power factor. For three phase AC, use the line-to-line voltage and multiply by the square root of three and the power factor.
The power factor is a number from 0 to 1. Motors often sit below 1, and the equipment's data plate or maker's sheet usually lists it. The power factor is ignored for DC.
Worked example
At 15 and 120, with a power factor of 0.9 and the supply set to Single phase AC, the power comes to 1,620 W.
Questions
Why multiply three phase by the square root of three?
Three phase power is spread over three lines that are offset from each other, and that factor adds them up correctly. Use line-to-line volts with it.
What is a typical power factor?
Heating elements are close to 1. Motors and some electronics are lower. Use the figure from the equipment's data sheet when you have one.
Does this give the breaker or wire size?
No. It gives power only. Wire and breaker sizes follow local electrical rules and need their own checks.
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