Electrical calculators

Amps to watts calculator

Watts = amps × volts. On AC, multiply by the power factor too, and for three-phase by √3 as well. Enter the current and the voltage to get watts, kilowatts and volt-amperes, with every step shown.

Calculated with electrician.wiki · https://electrician.wiki/calculators/amps-to-watts/

Result

P = 1,800 W (1.8 kW)

15 A at 120 V single-phase is 1,800 W (1.8 kW).

Real power (W): 1,800 W
Real power (kW): 1.8 kW
Apparent power (VA): 1,800 VA
Apparent power (kVA): 1.8 kVA
Formula used: P = V × I × PF

Show the work

1. Real power
$P = V \cdot I \cdot PF = 120 V \cdot 15 A \cdot 1 = 1,800 W$
2. Apparent power (what the wiring carries)
$S = V \cdot I = 120 V \cdot 15 A = 1,800 VA$
3. In kilowatts
$P = \frac{1,800 W}{1,000} = 1.8 kW$

Voltage and current are RMS values, as a true-RMS meter reads them.
Power factor is the true power factor (watts ÷ volt-amperes). On drives, LED drivers and other electronic loads the displacement figure (cos φ) can be higher than the true power factor.
The result is electrical input power. A motor delivers less at the shaft, by its efficiency.

New to this? Power factor explained

Report a problem with this result

How to convert amps to watts

To convert amps to watts, multiply the current by the voltage: watts = amps × volts. That gives the exact answer for DC and for resistive AC loads. For other AC loads multiply by the power factor as well, and for three-phase by √3 too.

Measure or read the current in amps. For milliamps, divide by 1,000.
Find the voltage: 5 V for USB, 12 or 24 V for vehicles, 120 or 240 V in North America, 230 V in most other countries.
Multiply amps by volts. For an AC motor or electronic load, multiply by its power factor too.
For a balanced three-phase load, multiply by √3 (about 1.732) as well, with the line-to-line voltage.

So 10 amps is 10 × 120 = 1,200 W on a 120 V circuit and 2,300 W at 230 V. A USB charger rated 2.4 A at 5 V delivers 12 W.

How to use the amps to watts calculator

This amps to watts calculator turns a current into power for DC, single-phase AC and three-phase AC circuits. It gives the real power in watts and kilowatts and, for AC, the apparent power in volt-amperes, which is what the cable, breaker and transformer actually carry. The working is shown under every result.

System. DC for batteries, solar strings and DC drives. Single-phase AC for ordinary 120, 230 or 240 V circuits, including a 208 V load connected between two phases. Three-phase AC for motors, rooftop units and feeders.
Current. For three-phase, the current in one line of a balanced load. A clamp-meter reading and a nameplate figure both work, but they answer different questions (see the mistakes below).
Voltage. For three-phase, say whether the figure is line-to-line (208, 400, 480 V) or line-to-neutral (120, 230, 277 V). The calculator flags the common mix-ups.
Power factor (AC only). Leave it at 1 for heaters, kettles and incandescent lamps. Induction motors run at about 0.8 to 0.9 at full load and well below that when lightly loaded. Electronic loads with power-factor correction are usually 0.9 or better; small LED lamps and chargers without it can be much lower.

Amps to watts formulas

Power is voltage times current. For DC that is the whole story. On AC, voltage times current gives the apparent power in volt-amperes; multiplying by the power factor gives the real power in watts, the part that becomes heat, light or shaft work.

P = V \cdot I

Single-phase AC

P = V \cdot I \cdot PF

Three-phase AC (balanced)

P = \sqrt{3} \cdot V_{LL} \cdot I \cdot PF = 3 \cdot V_{LN} \cdot I \cdot PF

Apparent power, single-phase and three-phase

S = V \cdot I

S = \sqrt{3} \cdot V_{LL} \cdot I

The √3 is not magic. Each phase of a balanced load delivers $V_{LN} \cdot I \cdot PF$ , so three phases deliver three times that. The line-to-line voltage is √3 times the line-to-neutral voltage (√3 × 277 V = 479.8 V, the nominal 480 V), so the same total can be written with √3 and the line-to-line voltage. Both forms give the same answer as long as each is paired with its own voltage. Divide watts by 1,000 for kilowatts.

Worked examples

Baseboard heaters on a 120 V circuit

A clamp meter reads 15 A on a 120 V circuit feeding resistance heaters. Resistance heating has a power factor of 1.

1. Real power
$P = V \cdot I \cdot PF = 120 V \cdot 15 A \cdot 1 = 1,800 W$
2. Apparent power (what the wiring carries)
$S = V \cdot I = 120 V \cdot 15 A = 1,800 VA$
3. In kilowatts
$P = \frac{1,800 W}{1,000} = 1.8 kW$

15 A at 120 V single-phase is 1,800 W (1.8 kW).

A heat pump outdoor unit on 240 V

The unit measures 18.5 A at 240 V, and the compressor runs at a power factor of about 0.9 at this load.

1. Real power
$P = V \cdot I \cdot PF = 240 V \cdot 18.5 A \cdot 0.9 = 3,996 W$
2. Apparent power (what the wiring carries)
$S = V \cdot I = 240 V \cdot 18.5 A = 4,440 VA$
3. In kilowatts
$P = \frac{3,996 W}{1,000} = 3.996 kW$

18.5 A at 240 V single-phase with power factor 0.9 is 3,996 W (3.996 kW); the apparent power is 4.44 kVA.

Line-to-neutral readings on a 208Y/120 V panel

You measured 120 V from each phase to neutral and 40 A in each line of a three-phase load. Choosing line-to-neutral saves converting to 208 V first, and gives the same answer.

1. Real power (line-to-neutral voltage)
$P = 3 \cdot V_{LN} \cdot I \cdot PF = 3 \cdot 120 V \cdot 40 A \cdot 0.95 = 13,680 W$
2. Apparent power (what the wiring carries)
$S = 3 \cdot V_{LN} \cdot I = 3 \cdot 120 V \cdot 40 A = 14,400 VA$
3. In kilowatts
$P = \frac{13,680 W}{1,000} = 13.68 kW$

40 A per line at 120 V line-to-neutral (207.8 V line-to-line) three-phase with power factor 0.95 is 13,680 W (13.68 kW); the apparent power is 14.4 kVA.

A 480 V three-phase air handler

The fan motor draws 42 A per line at 480 V with a power factor of 0.88.

1. Real power (line-to-line voltage)
$P = \sqrt{3} \cdot V_{LL} \cdot I \cdot PF = \sqrt{3} \cdot 480 V \cdot 42 A \cdot 0.88 = 30,728 W$
2. Apparent power (what the wiring carries)
$S = \sqrt{3} \cdot V_{LL} \cdot I = \sqrt{3} \cdot 480 V \cdot 42 A = 34,918 VA$
3. In kilowatts
$P = \frac{30,728 W}{1,000} = 30.73 kW$

42 A per line at 480 V three-phase with power factor 0.88 is 30,728 W (30.73 kW); the apparent power is 34.92 kVA.

A kettle on 230 V

A UK kettle drawing 13 A, the rating of its plug fuse. The element is resistive, so the power factor is 1.

1. Real power
$P = V \cdot I \cdot PF = 230 V \cdot 13 A \cdot 1 = 2,990 W$
2. Apparent power (what the wiring carries)
$S = V \cdot I = 230 V \cdot 13 A = 2,990 VA$
3. In kilowatts
$P = \frac{2,990 W}{1,000} = 2.99 kW$

13 A at 230 V single-phase is 2,990 W (2.99 kW).

A 400 V three-phase motor

A motor drawing 28 A per line at 400 V and power factor 0.86. This is electrical input; at about 90 % efficiency the shaft delivers roughly 15 kW.

1. Real power (line-to-line voltage)
$P = \sqrt{3} \cdot V_{LL} \cdot I \cdot PF = \sqrt{3} \cdot 400 V \cdot 28 A \cdot 0.86 = 16,683 W$
2. Apparent power (what the wiring carries)
$S = \sqrt{3} \cdot V_{LL} \cdot I = \sqrt{3} \cdot 400 V \cdot 28 A = 19,399 VA$
3. In kilowatts
$P = \frac{16,683 W}{1,000} = 16.68 kW$

28 A per line at 400 V three-phase with power factor 0.86 is 16,683 W (16.68 kW); the apparent power is 19.4 kVA.

Amps to watts conversion chart

These figures come from the same engine as the calculator. For a motor or other inductive load, multiply by its power factor. To go the other way, from a wattage to amps, use the watts to amps calculator.

Real power in watts at power factor 1. Three-phase columns use line-to-line voltage and the current in each line.
Amps	12 V DC	120 V 1-phase	230 V 1-phase	240 V 1-phase	208 V 3-phase	400 V 3-phase	480 V 3-phase
1 A	12	120	230	240	360.3	692.8	831.4
5 A	60	600	1,150	1,200	1,801	3,464	4,157
10 A	120	1,200	2,300	2,400	3,603	6,928	8,314
15 A	180	1,800	3,450	3,600	5,404	10,392	12,471
20 A	240	2,400	4,600	4,800	7,205	13,856	16,628
30 A	360	3,600	6,900	7,200	10,808	20,785	24,942
40 A	480	4,800	9,200	9,600	14,411	27,713	33,255
50 A	600	6,000	11,500	12,000	18,013	34,641	41,569
60 A	720	7,200	13,800	14,400	21,616	41,569	49,883
100 A	1,200	12,000	23,000	24,000	36,027	69,282	83,138

Amps to watts at 5, 12, 24 and 48 V DC

Battery, solar and USB ratings are usually given in amps, while loads are given in watts. On DC there is no power factor, so the conversion is a single multiplication. Remember that a battery’s voltage sags as it discharges, so the current for a fixed wattage rises towards the end.

Watts = amps × volts for DC. 5 V is USB; 12, 24 and 48 V are vehicle, solar and battery systems.
Amps	5 V DC	12 V DC	24 V DC	48 V DC
0.5 A	2.5	6	12	24
1 A	5	12	24	48
2 A	10	24	48	96
2.4 A	12	28.8	57.6	115.2
3 A	15	36	72	144
5 A	25	60	120	240
10 A	50	120	240	480
20 A	100	240	480	960
50 A	250	600	1,200	2,400
100 A	500	1,200	2,400	4,800

How many watts can a circuit carry?

Multiply the breaker rating by the voltage for the most a circuit can deliver, and use 80 % of that for anything that runs for three hours or more. These figures assume power factor 1; motor loads deliver fewer watts for the same current.

Watts at the breaker rating and at 80 % of it (a continuous load under the NEC), power factor 1.
Breaker	120 V, full	120 V, 80 %	240 V, full	240 V, 80 %
15 A	1,800	1,440	3,600	2,880
20 A	2,400	1,920	4,800	3,840
30 A	3,600	2,880	7,200	5,760
40 A	4,800	3,840	9,600	7,680
50 A	6,000	4,800	12,000	9,600
60 A	7,200	5,760	14,400	11,520

Mistakes that throw the answer off

Leaving the power factor at 1 for a motor. 10 A at 240 V is 2,400 W for a heater but 1,920 W for a motor at power factor 0.8. Using 1 overstates the motor’s real power by 25 %.
Pairing the wrong three-phase voltage with the formula. Using 277 V with √3 understates the power by 42 %; using 480 V with the factor 3 overstates it by 73 %. If you are not sure which voltage you have, the three-phase power calculator explains line and phase values for wye and delta systems.
Treating a 208 V single-phase load as three-phase. A water heater or condenser connected between two legs of a 208Y/120 V system is a single-phase load: P = 208 V × I × PF, with no √3.
Reading the nameplate as running current. Motor full-load amps are the current at full rated load. Air-conditioning nameplates list RLA and MCA, and MCA already includes 125 % of the largest motor for wire sizing. For energy use, measure under real load.
Measuring electronic loads with an average-responding meter. LED drivers, drives and switch-mode supplies draw distorted current that such meters misread. Use a true-RMS clamp for amps and a power meter if you need real watts.
Confusing input and output. The result is electrical input power. A motor’s horsepower or kW rating is the shaft output (1 hp = 746 W), which is lower by the motor’s efficiency.

Continuous loads and the 80 % figure

A 20 A circuit at 120 V carries 2,400 W at its full rating. A load that runs for three hours or more is a continuous load, and the NEC sizes the conductors and breaker for 125 % of it (210.19(A)(1) and 210.20(A)). Turned around, a continuous load may use only 80 % of the breaker: 16 A, which is 1,920 W at 120 V or 3,840 W at 240 V. When you are planning a circuit rather than measuring one, start from the wattage with the watts to amps calculator, size the conductor with the wire size calculator (or the IEC cable size calculator), and check long runs with the voltage drop calculator. For a transformer feeding the load, the transformer calculator gives full-load amps by kVA.

Method and verification

The calculator evaluates $P = k \cdot V \cdot I \cdot PF$ , where k is 1 for DC and single-phase, √3 for three-phase with line-to-line voltage and 3 with line-to-neutral voltage. DC ignores the power factor. Apparent power is the same product without the power factor. Everything is computed in double precision and rounded only for display: watts to the nearest watt from 1,000 W up and to four significant figures below that; kilowatts, kVA and volts to four significant figures.

The tests check eight cases worked by hand, from 10 A at 12 V DC to 100 A at 480 V and power factor 0.85 (70,668 W). They also check that line-to-neutral and line-to-line entries for the same system agree, that a round trip through the watts to amps calculator returns the starting current, and that zero, negative and out-of-range inputs are refused rather than answered. The underlying relationships are the ones in the Ohm’s law calculator, extended with the power factor for AC.

Assumes RMS values, a balanced three-phase load and the true power factor. Updated 2026-10-14. Found a problem? Report it and we log every fix publicly.

Questions people ask

How many watts is 1 amp?

120 W at 120 V, 230 W at 230 V and 240 W at 240 V. At 12 V DC it is 12 W, and at 5 V (USB) 5 W: watts are always amps times volts.

How many watts is 2.4 amps?

On a 5 V USB port, 12 W. At 12 V it is 28.8 W, and at 120 V 288 W.

How many watts is 10 amps?

1,200 W at 120 V, 2,300 W at 230 V and 2,400 W at 240 V, for a resistive load.

How many watts is 15 amps at 120 volts?

1,800 W for a resistive load such as a heater (15 A × 120 V). For a motor at power factor 0.8 the real power is 1,440 W, although the circuit still carries 1,800 VA.

How do I convert amps to watts for three-phase?

Multiply √3 (about 1.732) by the line-to-line voltage, the current in each line and the power factor. 100 A at 480 V and power factor 0.85 is 70,668 W, or 70.67 kW. With a line-to-neutral voltage, use 3 instead of √3.

Why does the power factor matter when converting amps to watts?

Because on AC, volts times amps gives volt-amperes, not watts. Motors and other inductive loads draw current that is partly out of step with the voltage; that part heats the wiring but does no work. The power factor is the share of the volt-amperes that is real power.

How many watts can a 20 amp circuit handle?

At 120 V, 2,400 W at the breaker’s full rating, or 1,920 W for a load that runs three hours or more (80 % of the rating). At 240 V the figures are 4,800 W and 3,840 W.

Are watts and volt-amperes the same?

Only when the power factor is 1, as with heaters and incandescent lamps. For anything else, volt-amperes are larger than watts. Generators, UPS units and transformers are rated in VA or kVA because their limit is current, whatever the power factor.