WeekendCalc

Amps to Watts Calculator

Enter the current in amps, the voltage and the type of circuit. You get the power in watts and kilowatts, and the apparent power in volt-amps.

Building in the UK? Use the UK (metric) version of this calculator.

Your project

A

For three-phase, the line-to-line voltage.

Use 1.00 for heaters and lights. Motors and some electronics are lower.

Results

Power
1,800 W
Power in kilowatts
1.800 kW
Apparent powerVolts × amps (× 1.732 for three-phase)
1,800 VA
Energy in one hourIf the load runs for an hour at this level
1.800 kWh
Safe continuous current (80% of the rating)If this is the breaker rating, the most a continuous load should draw
12.00 A
  • Watts = volts × amps for DC and for AC with a power factor of 1. For single-phase AC multiply also by the power factor, and for three-phase AC by 1.732 × the line voltage × current × the power factor. Electrical work is dangerous: follow your local code and use a licensed electrician.

How this calculator works

Watts are volts times amps. For DC and for AC loads with a power factor of 1 that is the whole sum. For AC loads with a power factor below 1, the watts doing work are the volt-amps times the power factor. For three-phase AC multiply by 1.732 and use the line-to-line voltage.

DC: W = V × A single-phase AC: W = V × A × PF three-phase AC: W = 1.732 × V × A × PF

Worked example: 15 A at 120 V is 1,800 W. A 15 A load at 240 V is 3,600 W. A 100 A load on a 12 V DC battery system is 1,200 W. A three-phase load of 30 A at 480 V and a power factor of 0.85 is 21.2 kW (24.9 kVA).

Amps to watts at common voltages

Single-phase AC at a power factor of 1, and 12 V DC.

Amps12 V DC120 V230 V240 V
5 A60 W600 W1,150 W1,200 W
10 A120 W1,200 W2,300 W2,400 W
15 A180 W1,800 W3,450 W3,600 W
20 A240 W2,400 W4,600 W4,800 W
30 A360 W3,600 W6,900 W7,200 W
40 A480 W4,800 W9,200 W9,600 W
50 A600 W6,000 W11,500 W12,000 W

Tips before you buy

  • A circuit breaker rating is the most the circuit can carry. Keep a continuous load to 80% of it: 12 amps on a 15 amp breaker, 16 amps on a 20 amp breaker.
  • Volt-amps (VA) and watts are the same only when the power factor is 1. A UPS or generator is rated in VA, and the watts it can supply are lower.
  • For DC, such as a 12 volt battery system, amps × volts is the power exactly: 100 amps at 12 volts is 1,200 watts.
  • Three-phase power gives more watts for the same current: 1.732 times as much at the same voltage.
  • Use the nameplate if you have it: it gives the amps or watts at the rated voltage.

Tools & materials for this project

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Clamp meterPlug-in power meter (Kill A Watt)Digital multimeterOutlet testerSurge protector power strip

Frequently asked questions

How do you convert amps to watts?

Multiply the amps by the volts. 15 A × 120 V = 1,800 W. For AC with a power factor below 1, multiply also by the power factor.

How many watts is a 15 amp circuit?

1,800 watts at 120 volts, and 1,440 watts for a load that runs continuously (80% of the rating).

How many watts is a 20 amp circuit?

2,400 watts at 120 volts, or 4,800 watts at 240 volts. For continuous use, 80% of that.

How many watts is 30 amps?

3,600 watts at 120 volts, 7,200 watts at 240 volts.

How many watts is 50 amps?

6,000 watts at 120 volts, 12,000 watts at 240 volts (a typical range or EV charger circuit).

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Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.