From the label to the circuit
Appliances list their power in watts, but circuits, fuses and breakers are rated in amps. Knowing the current tells you whether a heater, kettle or tool will fit on a circuit alongside everything else plugged into it.
This watts to amps converter divides power by voltage, with the power factor for AC loads and the √3 factor for three phase supplies. Switch modes to go the other way, from amps to watts.
How to use it
- Find the wattage on the appliance label or in its manual.
- Enter the supply voltage, such as 120 V in the US or 230 V in much of the world.
- Choose DC, single phase AC or three phase AC, and enter the power factor for AC if you know it.
- Read the current in amps, with the apparent power in volt-amperes.
The formulas
DC: amps = watts ÷ volts
single phase AC: amps = watts ÷ (volts × power factor)
three phase AC: amps = watts ÷ (√3 × volts × power factor)
and back: watts = volts × amps (× power factor, × √3 for three phase)Power factor describes how much of the current does useful work. Heaters, kettles and lamps with simple elements are close to 1. Motors and some electronics draw extra current that does no work, so their power factor is lower and they need more amps for the same watts.
Worked example: a 1,500 W heater on 120 V
- Single phase AC, power factor 1
- Current: 1,500 ÷ (120 × 1) = 12.5 A
The heater draws 12.5 A, a large share of a typical household circuit, so running a second big appliance on the same circuit could trip the breaker. On a 230 V supply, the same heater draws about 6.52 A.
Amps for common wattages
| Power | At 120 V | At 230 V |
|---|---|---|
| 100 W | 0.83 A | 0.43 A |
| 500 W | 4.17 A | 2.17 A |
| 1,000 W | 8.33 A | 4.35 A |
| 1,500 W | 12.5 A | 6.52 A |
| 2,000 W | 16.67 A | 8.7 A |
Higher voltage means less current for the same power, which is why large equipment and long cable runs often use higher voltages.
Adding up a circuit
To see whether several appliances can share a circuit, convert each to amps and add them up, then compare the total with the breaker or fuse rating. Motors draw a brief surge when they start, well above their running current, which is why a fridge or a power tool can trip a breaker that copes with it once running.
Related tools
- For volts, amps, ohms and watts together, see the Ohm’s law calculator.
- For a long run of cable, check the voltage drop calculator.
- For running costs, the electricity cost calculator turns watts and hours into money.
Frequently asked questions
How do I convert watts to amps?
Divide the watts by the volts. A 1,200 W microwave on 120 V draws 10 A. For AC motors and other loads with a power factor below 1, divide by volts times the power factor. For three phase supplies, also divide by √3, about 1.732.
How many amps is 1,500 watts?
At 120 V, 1,500 watts is 12.5 amps; at 230 V it is about 6.52 amps; at 12 V DC it is 125 amps. The current depends on the voltage, which is why the same appliance draws very different currents on different supplies. Enter your own voltage above.
How do I convert amps to watts?
Multiply the amps by the volts, and by the power factor for AC loads. Ten amps at 230 V with a power factor of 1 is 2,300 watts. For three phase, multiply by √3 as well. Choose Amps to watts above to work it out for any supply.
What is power factor?
Power factor is the share of the current that does useful work, from 0 to 1. Simple heating elements are close to 1. Motors and some power supplies are lower, so they draw more current than watts alone suggest. If you do not know it, 1 gives the smallest current.
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