LumaQuote Electrical calculators Watts to amps

Watts to Amps Calculator

Convert watts to amps for single-phase, three-phase and DC circuits. Enter the power and the voltage, and the current updates as you type, with the formula and your numbers shown.

How to convert watts to amps

Current is power divided by voltage. On AC circuits the power factor goes in the bottom of the equation too, and three-phase adds the square root of 3 (1.732).

DC: amps = watts ÷ volts

Single-phase AC: amps = watts ÷ (volts × power factor)

Three-phase AC: amps = watts ÷ (1.732 × line-to-line volts × power factor)

Examples

1,500 W heater at 120 V: 1,500 ÷ 120 = 12.5 A. The same heater on 240 V draws 6.25 A.
2,000 W of LED lighting on a 277 V circuit, power factor 0.9: 2,000 ÷ (277 × 0.9) = 8.02 A.
10 kW three-phase load at 480 V, power factor 0.9: 10,000 ÷ (1.732 × 480 × 0.9) = 13.36 A in each line.

Watts to amps chart

Current at common voltages, power factor 1.0. For loads with a lower power factor, divide the amps shown by the power factor.

Watts	120 V	208 V	240 V	277 V	208 V 3-phase	480 V 3-phase
100 W	0.83 A	0.48 A	0.42 A	0.36 A	0.28 A	0.12 A
250 W	2.08 A	1.20 A	1.04 A	0.90 A	0.69 A	0.30 A
500 W	4.17 A	2.40 A	2.08 A	1.81 A	1.39 A	0.60 A
750 W	6.25 A	3.61 A	3.13 A	2.71 A	2.08 A	0.90 A
1,000 W	8.33 A	4.81 A	4.17 A	3.61 A	2.78 A	1.20 A
1,500 W	12.50 A	7.21 A	6.25 A	5.42 A	4.16 A	1.80 A
2,000 W	16.67 A	9.62 A	8.33 A	7.22 A	5.55 A	2.41 A
2,500 W	20.83 A	12.02 A	10.42 A	9.03 A	6.94 A	3.01 A
3,000 W	25.00 A	14.42 A	12.50 A	10.83 A	8.33 A	3.61 A
4,000 W	33.33 A	19.23 A	16.67 A	14.44 A	11.10 A	4.81 A
5,000 W	41.67 A	24.04 A	20.83 A	18.05 A	13.88 A	6.01 A
7,500 W	62.50 A	36.06 A	31.25 A	27.08 A	20.82 A	9.02 A
10,000 W	83.33 A	48.08 A	41.67 A	36.10 A	27.76 A	12.03 A

Three-phase columns use the line-to-line voltage and give the current per line.

Why power factor matters

Watts are the power a load actually uses. The wire and the breaker carry volt-amps. When the power factor is below 1.0, the current is higher than watts ÷ volts suggests, and that higher current is what heats the conductors and trips the breaker.

1.0: heaters, incandescent lamps and other resistive loads.
0.9 to 0.95: most LED drivers and electronic fluorescent ballasts at full load. Check the spec sheet.
0.8 to 0.9: motors and mixed loads. Use the nameplate current for motors when you have it.

Common mistakes

Using lamp watts instead of input watts. A 400 W metal halide draws about 458 W with its ballast. A 2-lamp T8 fixture draws about 59 W. Use the input watts, which is what the circuit sees.
Leaving out 1.732 on three-phase. Without it the answer is 73% too high.
Using 240 V for a 208 V building. Many commercial buildings are 208Y/120 V. A 240 V appliance on 208 V draws different current, and heaters put out less heat.
Sizing the breaker to the exact amps. Loads that run 3 hours or more are continuous, so the breaker has to be at least 125% of the current. The breaker size calculator does that step.

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Watts to amps FAQ

How many amps is 1500 watts?

12.5 A at 120 V and 6.25 A at 240 V, for a resistive load like a space heater. A 1,500 W heater runs for hours, so treat it as a continuous load: it needs a 20 A circuit at 120 V.

How many amps is 1000 watts at 120 volts?

8.33 A at power factor 1.0. For a load with a power factor of 0.9, it is 9.26 A.

How do you convert watts to amps on three-phase?

Divide the watts by 1.732 × the line-to-line voltage × the power factor. A 10 kW load at 480 V and power factor 0.9 draws 13.36 A per line.

Can I convert watts to amps without the voltage?

No. The same power draws twice the current at half the voltage, so you need the voltage. For AC loads you also need the power factor, or you can use 1.0 for heaters and incandescent lamps.

How many watts can a 20 amp circuit handle?

2,400 W at 120 V in theory. For continuous loads such as lighting, the limit is 80%, which is 1,920 W at power factor 1.0. See the lighting circuit calculator for fixture counts.

What power factor should I use?

1.0 for resistive loads, about 0.9 for LED and fluorescent lighting, and 0.8 to 0.9 for motors and mixed loads. The nameplate or spec sheet value is always better than a typical one.