How many watts is 20 amps?

2,400 W at 120 V, 4,800 W at 240 V, both at PF 1. A 20 A circuit loaded continuously should carry no more than 16 A (80 %), so 1,920 W at 120 V.

Watts or volt-amperes?

Watts are real power (heat, motion, light); volt-amperes are what the wiring carries. They are equal at PF 1 and differ by the power factor otherwise. Breakers and conductors are sized on amps, so on VA.

Amps to watts calculator

Power · single-phase4,800WP = V × I × PF20 A at 240 V, PF 1.00

Current

Per line

Voltage

120, 240, or a DC value

Phase

Power factor

1 for heaters and resistive loads; 0.8–0.9 for motors

Kilowatts: 4.80 kW
Apparent powervolts × amps (× √3 for three-phase), before the power factor: 4,800 VA
Per hour at full load: 4.80 kWh

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Amps and volts give watts: P = V × I for DC and resistive loads, times the power factor for AC, times √3 for balanced three-phase at line-to-line voltage. The tally shows kilowatts, the apparent power in VA before the power factor, and the energy per hour at full load.

Worked examples

20 A at 240 V: 4,800 W, 4.8 kW: the full continuous rating of a 20 A 240 V circuit, before the 80 % rule. Open this run
15 A at 120 V: 1,800 W. A 15 A circuit can supply 1,800 W momentarily and 1,440 W continuously (80 %). Open this run
30 A three-phase at 208 V, PF 0.9: P = √3 × 208 × 30 × 0.9 = 9,727 W; apparent power 10.8 kVA. Open this run
100 A at 12.6 V (DC): 1,260 W: what a 100 A alternator delivers at full output. Open this run

How it is worked out

DC: P = V × I. Single-phase AC: P = V × I × PF. Three-phase (balanced): P = √3 × V × I × PF with V line-to-line.

Apparent power S = V × I (× √3) in VA; kWh per hour = kW at full load for one hour.

The figures behind it

Power formulas: P = V × I × PF and P = √3 × V × I × PF; arithmetic, no table.

Questions people ask

How many watts is 20 amps?: 2,400 W at 120 V, 4,800 W at 240 V, both at PF 1. A 20 A circuit loaded continuously should carry no more than 16 A (80 %), so 1,920 W at 120 V.
Watts or volt-amperes?: Watts are real power (heat, motion, light); volt-amperes are what the wiring carries. They are equal at PF 1 and differ by the power factor otherwise. Breakers and conductors are sized on amps, so on VA.

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