Amps to Watts Calculator: Convert Amps to Watts at 120 V or 240 V

Watts = amps × volts. 1 amp is 120 watts on a US household circuit and 240 watts on a 240 V circuit, so 15 A at 120 V is 1,800 W and 30 A at 240 V is 7,200 W. For motors and electronics, multiply by the power factor as well.

Amps to watts formula

watts     = amps × volts × power factor
kilowatts = watts ÷ 1,000
3-phase:  watts = amps × volts × 1.732 × power factor

For heaters, kettles, toasters and incandescent bulbs, the power factor is 1 and watts are simply amps times volts. Motors, compressors and many power supplies draw current slightly out of step with the voltage, so the real power is lower than volts × amps; a refrigerator or a pump typically has a power factor of 0.8–0.95. A clamp meter reading of 5 A on a 120 V fridge therefore means about 480–570 W, not 600 W.

Amps to watts chart

Power factor 1. US homes have 120 V circuits and 240 V circuits; 208 V is what you get between two legs of a three-phase supply in apartments and commercial buildings; 12 V is a car or RV battery system.

Amps	12 V DC	120 V	208 V	240 V
1 A	12	120	208	240
5 A	60	600	1,040	1,200
10 A	120	1,200	2,080	2,400
13 A	156	1,560	2,704	3,120
15 A	180	1,800	3,120	3,600
16 A	192	1,920	3,328	3,840
20 A	240	2,400	4,160	4,800
24 A	288	2,880	4,992	5,760
30 A	360	3,600	6,240	7,200
40 A	480	4,800	8,320	9,600
50 A	600	6,000	10,400	12,000

Kilowatts to amps

Going the other way, a load rated in kW draws amps = kW × 1,000 ÷ volts. That is how a 7.2 kW EV charger draws 30 A at 240 V, and why it goes on a 40 A breaker: continuous loads are sized at 125%.

Load	Amps at 120 V	Amps at 240 V
1 kW	8.3	4.2
5 kW	41.7	20.8
7.2 kW	60.0	30.0
11.5 kW	95.8	47.9
22 kW	183.3	91.7

How many watts can a circuit carry?

A 15 A circuit at 120 V carries 1,800 W, and a 20 A circuit 2,400 W. If the load runs for three hours or more (a space heater, an EV charger, a dehumidifier), NEC 210.20(A) limits it to 80% of the breaker: 1,440 W on a 15 A circuit and 1,920 W on a 20 A circuit. That is why 1,500 W is the largest plug-in heater sold in the US. The full breaker table is in the watts to amps calculator, and every size is explained in standard breaker sizes.

Common questions

How many watts is 1 amp?

120 watts at 120 V, 240 watts at 240 V, and 12 watts at 12 V. Watts = amps × volts.

How many watts is 15 amps?

1,800 W at 120 V. For a load that runs three hours or more, keep it to 1,440 W (80%).

How many watts is 20 amps?

2,400 W at 120 V and 4,800 W at 240 V. Continuous loads: 1,920 W at 120 V.

How many watts is 30 amps at 240 volts?

7,200 W, which is why a 30 A generator inlet (L14-30) tops out at 7,200 W however big the generator is.

How do I convert amps to kW?

Multiply amps by volts and divide by 1,000. 40 A × 240 V = 9,600 W = 9.6 kW.

Guides that use this calculator

Updated October 10, 2026 by Biel Vazquez · Sources: DOE Energy Saver, NEC Table 310.16 (2023)

Amps to watts calculator