Watts to Amps Calculator

Convert watts to amps for DC, single-phase or three-phase AC at any voltage and power factor, with the same load worked out from 12 V to 400 V.

Amps are watts divided by volts. A 1,500 W space heater draws 12.5 A on a 120 V US circuit, but only 6.52 A at 230 V in the UK or Australia. For AC loads that aren't purely resistive, divide by the power factor as well: 1,000 W at 230 V with a power factor of 0.8 draws 5.43 A. On three-phase, divide by √3 too: a 10 kW load at 400 V with a power factor of 0.9 draws 16.04 A per line. This calculator converts watts or kilowatts to amps for DC, single-phase AC and three-phase AC at any voltage and power factor. It also shows the apparent power in VA, and what the same load would draw at 12, 24, 48, 120, 208, 230, 240 and 400 V.

Mains
V
Current
12.5 A

at 120 V

Power
1,500 W

1.5 kW

Apparent power
1,500 VA

1.5 kVA

How it was worked out
  1. Single-phase AC: I = P ÷ (V × PF)
  2. 1,500 W ÷ (120 V × 1) = 12.5 A
Voltage1,500 W draws
12 V125 A
24 V62.5 A
48 V31.25 A
120 V12.5 A
208 V7.21 A
230 V6.52 A
240 V6.25 A
400 V3.75 A
480 V3.13 A

Power factor is 1 for heaters, kettles and incandescent bulbs, and lower (often 0.8 to 0.95) for motors, compressors and some power supplies; the label or manual may give it. Three-phase uses the voltage between lines (208 or 480 V in the US, 400 V in the UK and Australia). Appliance labels usually give the most power drawn, so everyday current is often lower.

Common use cases

  • Check how many amps an appliance draws before plugging it into a circuit
  • Add up loads to see whether they'll trip a breaker
  • Work out the current from a battery, inverter or solar panel
  • Convert a motor's kW rating to full-load amps on single or three-phase

How to use

  1. Leave the converter on watts to amps, or switch to amps to watts.
  2. Pick DC, single-phase AC or three-phase AC. The voltage fills in for your country, and you can change it.
  3. Enter the power in watts or kilowatts.
  4. For AC, enter the power factor: 1 for heaters and kettles, lower for motors.
  5. Read the current, and the same load at other voltages in the table.

FAQ

How many amps is 1,000 watts?

8.33 A at 120 V, 4.35 A at 230 V and 4.17 A at 240 V, for a load with a power factor of 1 such as a heater.

How many watts can a 15 A or 20 A circuit handle?

At 120 V, a 15 A circuit carries up to 1,800 W and a 20 A circuit 2,400 W. Loads that run for 3 hours or more should stay at 80% of that, 1,440 W and 1,920 W, because the NEC sizes circuits at 125% of continuous loads.

What is power factor?

Power factor is the share of the current that does useful work. Heaters, kettles and incandescent bulbs have a power factor of 1, so amps are simply watts ÷ volts. Motors, compressors and some electronics draw extra current that doesn't do work, so their power factor is lower, often 0.8 to 0.95, and they draw more amps for the same watts.

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

Divide the watts by √3 (1.732) times the line-to-line voltage times the power factor. 10,000 W at 400 V and a power factor of 0.9 is 10,000 ÷ (1.732 × 400 × 0.9) = 16.04 A. At 208 V it's 30.84 A.

How many amps does 100 W draw at 12 V?

100 ÷ 12 = 8.33 A. Low-voltage DC needs a lot more current for the same power, so cable size and voltage drop matter more.

Related tools

Results are worked out from the figures you enter, for information only. They are not electrical, engineering or professional advice. Mains electricity can kill and start fires. Check cable and circuit sizes against the wiring rules where you live (the NEC and local amendments in the US, BS 7671 in the UK, AS/NZS 3000 and 3008 in Australia and New Zealand), and use a licensed electrician where the law requires one.