Watts to amps calculator, and amps to watts.

To convert watts to amps, divide the watts by the volts. A 1,500 W heater on 120 V draws 1,500 ÷ 120 = 12.5 amps. For AC the power factor matters too, and for three phase there is a square root of 3 in the sum. This watts to amps calculator does all three and goes the other way as well, from amps to watts, and from kW or kVA to amps, with the working shown.

How to use the watts to amps calculator

1. Pick the Current type: "DC", "AC single phase" or "AC three phase, line to line".
2. Pick what to Find: "Amps, from watts, kW or kVA", "Watts, kW and kVA, from amps", or "Volts, from power and amps".
3. Type the Power and pick its Unit. Use W or kW for real power. Use VA or kVA for apparent power, which is what a transformer or generator is often rated in.
4. Type the Voltage, or press a preset such as 12 V, 120 V, 230 V, 240 V or 400 V 3-phase. The three phase buttons also switch the Current type.
5. For AC, type the Power factor, or press 1, 0.95, 0.9, 0.85 or 0.8. If you do not know it, 1 is the figure for a plain resistive load such as a heating element.
6. Read the big result, the other values in the cards, the working under them, and the table of the same load at other voltages. "Copy result" and "Copy link" keep the answer.

The formulas

P is real power in watts, V is the voltage, I is the current in amps and PF is the power factor. For kVA the power factor drops out: I = S ÷ V for single phase and I = S ÷ (√3 × V) for three phase, where S is the apparent power in VA. Real power is apparent power times the power factor, so kW = kVA × PF.

Worked examples

• DC. 120 W on 12 V: 120 ÷ 12 = 10 A.
• Watts to amps, single phase. 1,500 W on 120 V with a power factor of 1: 1,500 ÷ 120 = 12.5 A. With a power factor of 0.9: 1,500 ÷ (120 × 0.9) = 13.89 A.
• kW to amps. 3 kW is 3,000 W. On 230 V with a power factor of 1: 3,000 ÷ 230 = 13.04 A.
• kW to amps, three phase. 10 kW on 400 V with a power factor of 0.8: 10,000 ÷ (1.7321 × 400 × 0.8) = 18.04 A.
• kVA to amps. 50 kVA three phase on 400 V: 50,000 ÷ (1.7321 × 400) = 72.17 A. 10 kVA single phase on 240 V: 10,000 ÷ 240 = 41.67 A.
• Amps to watts. 20 A on 240 V single phase with a power factor of 0.95: 240 × 20 × 0.95 = 4,560 W, or 4.56 kW. The apparent power is 240 × 20 = 4,800 VA.

Why the voltage changes the amps

For the same watts, a higher voltage means fewer amps. 1,500 W is 125 A at 12 V, 31.25 A at 48 V and 12.5 A at 120 V. The table under the result shows the load at nine voltages, so you can compare them. The presets are only numbers: your supply, your country and your equipment decide the voltage, so read the label.

Power factor and three phase

Power factor is real power divided by apparent power, a number from 0 to 1. A plain heating element has a power factor of 1. Motors and some power supplies have a lower one, and the nameplate or data sheet often states it. The three phase formula here uses the voltage between two lines. If a label gives the voltage from one line to neutral, multiply it by the square root of 3 first.

kW and kVA are not the same

Kilowatts measure the real power that does the work. Kilovolt-amps measure the apparent power, volts times amps, which is what the wiring and the supply have to carry. They match only when the power factor is 1. A load of 8 kW at a power factor of 0.8 is 8 ÷ 0.8 = 10 kVA, so it draws the same current as a 10 kVA load at a power factor of 1. That is why kVA to amps and kW to amps give different answers for the same number.

Safety

The result is a calculation, not an electrical design. The amps a load draws are only one input to choosing wire, breakers and other protection. Those choices follow local electrical code, and a licensed electrician should make them. This page gives no wire sizes on purpose.

To change units like kilowatts, horsepower or watt-hours, use the unit converter, which has Power and Energy groups. To work out a percent of a rating, like 80% of a breaker's amps, the percentage calculator does it in one step. For speeds and distances, see the velocity calculator.