Electrical units and conversion

Watts to amps and amps to watts calculator

Convert watts to amps or amps to watts at your supply voltage — switch direction in the calculator — with the power factor shown instead of silently assumed.

How do you convert watts to amps, and amps to watts?

Amps = watts ÷ (volts × power factor), and watts = amps × volts × power factor. Both need the voltage. For a resistive load the power factor is 1, so 1,500 W draws 12.50 A at 120 V, and 10 A at 120 V is 1,200 W. Volts alone cannot be converted to watts — you need the current too: watts = volts × amps. For a motor-driven load at a power factor of 0.8, the same 1,500 W draws 15.63 A at 120 V — 25% more current for the same work.

Your inputs

Direction

Power

Supply voltage

Nominal supply voltage. 120 V and 240 V are the North American single-phase values; most of Europe, the UK and Australia use 230 V.

Common supply voltages

Type of load

Sets the power factor used below: 1.00.

12.50

amps at 120 V

1.5 kW drawn at a power factor of 1.00

Exact given your inputs

Current: 12.50 A
Real power: 1.5 kW
Apparent power: 1,500 VA
Fits a breaker of: 20 A

Why the power factor is on this page at all

A purely resistive load draws current in phase with the voltage, so the power factor is 1 and watts ÷ volts is exact. At a power factor of 1 the volt-amps and the watts are the same number, so watts ÷ volts is the complete answer. Switch the load type above to see how far apart they move for a motor.

What the breaker column means, and what it does not

A circuit serving a continuous load may be loaded to 80% of its breaker rating, so 12.50 A needs at least a 20 A circuit on that basis alone. This is arithmetic, not a wiring design: conductor size, ambient temperature, derating, other loads on the same circuit and local code all change the answer. Do not size a circuit from this page.

Method

1500 W ÷ (120 V × 1) = 12.5 A
120 V × 12.5 A = 1500 VA apparent power

Engine currentEngine-1.0.0. Values are computed at full precision and rounded only for display.

Assumptions

Single-phase AC (or DC) at 120 V nominal. Real supply voltage varies, and current moves inversely with it: the same load draws more amps on a sagging supply.
Power factor of 1, so watts and volt-amps are the same number. This holds for resistive loads only.
Steady running current. Motor starting current is several times this figure for a fraction of a second and is not included here.

What can change the result?

Actual supply voltage, which sags under load and varies by region and time of day
Real power factor of your specific unit, which changes with how heavily it is loaded
Motor starting current, which is several times the running figure for a fraction of a second
Whether the nameplate lists maximum draw or typical draw — most list the maximum

Amps to watts at the common supply voltages

The reverse direction: watts = amps × volts at a power factor of 1. This is also the answer to "volts to watts" — multiply the voltage by the current the device draws.

Watts = amps × volts at a power factor of 1. Computed by currentEngine-1.0.0 and rounded to whole watts.
Current	120 V	230 V	240 V
1 A	120 W	230 W	240 W
5 A	600 W	1,150 W	1,200 W
10 A	1,200 W	2,300 W	2,400 W
15 A	1,800 W	3,450 W	3,600 W
20 A	2,400 W	4,600 W	4,800 W
30 A	3,600 W	6,900 W	7,200 W

Watts to amps at the common supply voltages

Resistive loads only, where the power factor is 1. Read down a column to see why the same appliance rating produces roughly half the current on a 230 V supply as on a 120 V one: the current falls in direct proportion to the voltage, while the work done stays the same.

Amps = watts ÷ volts at a power factor of 1. Computed by currentEngine-1.0.0 and rounded to two decimals for display.
Power	120 V	230 V	240 V
100 W	0.83 A	0.43 A	0.42 A
500 W	4.17 A	2.17 A	2.08 A
1,000 W	8.33 A	4.35 A	4.17 A
1,500 W	12.50 A	6.52 A	6.25 A
2,000 W	16.67 A	8.70 A	8.33 A
3,000 W	25.00 A	13.04 A	12.50 A
5,000 W	41.67 A	21.74 A	20.83 A

The same 1,000 W, three different currents

Most watts-to-amps converters divide by the voltage and stop. That is correct for a heater and wrong for a fridge. Watts measure work actually done; the supply has to deliver volt-amps, and for anything with a motor in it those two numbers are not the same. The last column is the extra current that upstream equipment must carry, even though the real power is unchanged.

1,000 W at 120 V under three load types. Typical power factors; your specific unit may differ, and a lightly loaded motor is usually worse.
Load type	Power factor	Current	Apparent power	Extra current vs PF 1
Resistive	1.00	8.33 A	1,000 VA	+0.0%
Motor-driven	0.80	10.42 A	1,250 VA	+25.0%
Switch-mode electronics	0.95	8.77 A	1,053 VA	+5.3%

What this page does not tell you

It does not size a circuit. The engine reports the smallest common breaker whose continuous-load allowance of 80% covers the current, because that is a useful sanity check, but a real circuit also depends on conductor size, cable run length, ambient temperature, grouping with other cables, what else shares the circuit, and the code in force where you live. Treat the figure as arithmetic that tells you when something is obviously too big for a circuit, never as a design.

It also reports steady running current. A motor drawing 1.56 A while running can pull several times that for a fraction of a second at start-up. That surge rarely trips a breaker, because breakers tolerate brief overloads by design, but it matters a great deal for inverters and generators, which do not.