Amps to Watts Calculator: DC, AC and 3-Phase
Convert amps to watts for DC, single-phase AC and three-phase AC circuits at any voltage and power factor. Shows the formula P = V × I × PF and worked examples.
Fill in every field to see the result.
Results are ideal-circuit estimates: they ignore wire resistance, reactance and losses. In three-phase circuits the voltage is the line-to-line voltage.
About the Amps to Watts Calculator
The Amps to Watts Calculator works out the real power a circuit delivers from the current it carries. Type the current in amps, choose DC, single-phase AC or three-phase AC, and type the voltage. For AC circuits, also type the power factor. The page opens on the power converter with amps to watts already selected, and you can switch to watts to amps, kVA to amps, amps to kVA or kVA to kW without losing what you typed.
Amps alone do not tell you the power. You always need the voltage too, because power is current times voltage. For AC loads such as motors, the power factor also matters: part of the current only charges and drains the load's magnetic or electric field and does no useful work.
The result is an ideal-circuit estimate. It does not include cable losses, starting surges or reactance, so check the rating plate of the appliance before you choose a fuse or a breaker.
The formulas
With V the voltage, I the current and PF the power factor:
In a three-phase circuit, V is the line-to-line voltage, measured between two phases: 400 V in most of Europe and 480 V or 208 V in North America.
Worked examples
DC
A 12 V car accessory drawing 5 A uses 12 × 5 = 60 W. A 120 V DC supply carrying 5 A delivers 600 W.
Single-phase AC
A 10 A load on 230 V with a power factor of 1, such as a heater, uses 2,300 W. The same current into a motor with a power factor of 0.8 delivers only 1,840 W of real power.
Three-phase AC
A motor drawing 10 A per phase on 400 V with a power factor of 0.85 uses √3 × 400 × 10 × 0.85 = 5,888.97 W, or about 5.89 kW.
Common values at 120 V and 230 V
At a power factor of 1, 1 A is 120 W on a 120 V supply and 230 W on a 230 V supply. So 5 A is 600 W or 1,150 W, 10 A is 1,200 W or 2,300 W, 13 A is 1,560 W or 2,990 W, 15 A is 1,800 W or 3,450 W, and 20 A is 2,400 W or 4,600 W.
Why the power factor matters
A power factor below 1 means the current and the voltage are out of step. The wires still carry the full current and get just as warm, but less of it turns into useful power. That is why cables and breakers are sized by current, not by watts, and why utilities charge large sites for a poor power factor.
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Related tools
Go the other way with the Watts to Amps Calculator, or size a generator or transformer with the kVA to Amps Calculator. The full Ohm's Law Calculator also solves resistance.
Frequently asked questions
How do I convert amps to watts?
Multiply the current by the voltage, and for AC loads by the power factor too. On a 230 V supply, 10 A with a power factor of 1 is 2,300 W of real power.
How many watts is 15 amps?
It depends on the voltage. At 120 V and a power factor of 1, 15 A is 1,800 W; at 230 V the same current is 3,450 W. Type your own voltage to see the figure.
Do I need the power factor for DC?
No. Direct current has no phase shift between voltage and current, so the power is simply volts times amps and the calculator hides the power factor field for DC.
What is a typical power factor?
Heaters, kettles and incandescent lamps are close to 1. Induction motors run between about 0.7 and 0.9, and many electronic power supplies with correction reach 0.95 or more.
How do I convert amps to watts in three-phase?
Multiply the line current by the line-to-line voltage, the power factor and the square root of three. At 400 V, 10 A per line with a power factor of 0.85 is about 5,889 W.