Watts to Amps Calculator: DC, AC and 3-Phase
Convert watts to amps for DC, single-phase AC and three-phase AC at a stated voltage and power factor. Shows the formula I = P ÷ (V × 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 Watts to Amps Calculator
The Watts to Amps Calculator tells you how much current a load draws from its power rating. Type the power in watts, choose DC, single-phase AC or three-phase AC, type the supply voltage and, for AC, the power factor. The page opens on the power converter with watts to amps already selected; switch the direction at any time to convert amps to watts, kVA to amps, amps to kVA or kVA to kW.
Knowing the current is the first step in choosing a cable, a fuse or a circuit breaker, and in checking whether a socket or an extension lead can take a load. Remember that the result is an ideal-circuit estimate. Motors and compressors draw several times their running current for a moment when they start, and the calculator does not include that surge or any cable losses.
The formulas
With P the real power, V the voltage and PF the power factor:
For three-phase supplies, V is the line-to-line voltage, such as 400 V or 480 V. The result is the current in each line.
Worked examples
A kettle on 230 V
A 2,000 W kettle with a power factor of 1 draws 2,000 ÷ 230 = 8.69565 A, which fits on a 13 A plug.
A motor on 230 V
A 2,000 W motor with a power factor of 0.9 draws 2,000 ÷ (230 × 0.9) = 9.66184 A. The lower the power factor, the more current the same power needs.
A space heater on 120 V
A 1,500 W heater on a 120 V outlet draws 1,500 ÷ 120 = 12.5 A, which is why two heaters on one 15 A circuit trip the breaker.
A three-phase load
A 15 kW three-phase heater on 400 V with a power factor of 1 draws 15,000 ÷ (√3 × 400) = 21.6506 A per line.
Common values
At a power factor of 1, 100 W draws 0.833 A at 120 V and 0.435 A at 230 V. 1,000 W draws 8.33 A at 120 V and 4.35 A at 230 V. 3,000 W draws 25 A at 120 V and 13.04 A at 230 V.
Reading a rating plate
Appliance plates usually give the power in watts and the voltage. If a plate gives volt-amperes (VA) instead, use the kVA to amps direction, because VA already includes the power factor. When a plate gives both the watts and the amps, the ratio tells you its power factor.
Privacy
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Related tools
Convert back with the Amps to Watts Calculator, work from kVA with the kVA to Amps Calculator, or solve resistance too in the Ohm's Law Calculator.
Frequently asked questions
How do I convert watts to amps?
Divide the power by the voltage, and for AC loads also by the power factor. A 2,000 W load on 230 V with a power factor of 0.9 draws 9.66 A.
How many amps does a 1500 W heater draw?
On a 120 V outlet it draws 1,500 ÷ 120 = 12.5 A. On a 230 V supply it draws about 6.52 A, because the higher voltage needs less current for the same power.
Why does a low power factor raise the current?
With a power factor below 1, part of the current does no useful work, so more total current is needed to deliver the same real power. The calculator divides by the power factor for that reason.
Can I use this to pick a breaker?
It gives the running current only, which is a starting point. Breakers and cables are chosen under local wiring rules that add margins for starting surges, grouping and temperature.
What voltage should I use for three-phase loads?
Use the line-to-line voltage, such as 400 V or 480 V, and choose Three-phase AC. The result is the current in each of the three supply lines, not the total of all three.