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Electrical

Amps to Watts Calculator

Convert current to power, single or three phase.

Your measurementsEvery assumption editable01

1.0 for heaters and lamps, around 0.8 for motors.

PowerCalculated live02

Result

4800W

20 A at 240 V draws 4800 W

Current
20 A
Voltage
240 V
Phase
Single phase
Apparent powerV × I
4800 VA
Real powerat 1 power factor
4800 W
In kilowatts
4.8 kW
Mechanical equivalent746 W per horsepower
6.434 hp

Watts is real power — the part doing useful work. Volt-amps is apparent power, which is what the conductors and the breaker actually carry. On a resistive load they are equal; on a motor they are not, and it is the volt-amps that determines the wire size.

The √3 on three phase comes from the 120-degree relationship between the legs, not from a correction factor. Using the single-phase formula on a three-phase supply understates the power by about forty-two per cent.

The horsepower figure is the mechanical equivalent of the electrical power, not a motor's shaft output. A real motor loses some of it to heat, which is what its efficiency rating describes.

The reverse of watts to amps, and a separate question in practice — you usually know the breaker or the measured current and want to know the load. Power factor and phase both change the answer.

Why use this tool?What it does differently03

Why use this tool?

Both phase configurations

The three-phase form multiplies by √3, which is a 73% difference — not a rounding detail.

Real and apparent power

Watts and volt-amps side by side, since conductors carry the volt-amps.

Horsepower equivalent

For comparing against motor ratings.

Power factor explained

Why a motor draws more current than its wattage implies.

How this worksThe method04

How this amps to watts calculator works

Apparent power is voltage times current, or √3 times that on three phase. Real power is apparent power times the power factor.

On a resistive load — a heater, an incandescent lamp — power factor is one and the two figures match exactly. On anything with a motor or a switching supply it does not, and the gap is current the conductors carry without doing useful work.

The horsepower figure is the mechanical equivalent of that electrical power at 746 watts per horsepower. It is not a motor’s shaft output, which is lower by its efficiency.

How to use itStep by step05

How to use it

  1. Step 1: Enter the current

    Measured, or the rating of the circuit you are working from.

  2. Step 2: Enter the voltage

    Line voltage for three phase.

  3. Step 3: Set the power factor

    1.0 for resistive loads, around 0.8 for motors.

  4. Step 4: Select the phase

    This changes the formula, not just a constant.

Example usageWorked figures06

Example usage

A 240 V circuit
20 A at 240 V with unity power factor is 4,800 W — 4.8 kW, or about 6.43 hp equivalent.
A motor load
The same 20 A at 0.8 power factor delivers only 3,840 W of real power, though the conductors still carry the full 4,800 VA.
Three phase
20 A at 480 V three phase is 16,627 VA — more than three times the single-phase 240 V figure for the same current.
Frequently asked questionsCommon questions07

Frequently asked questions

How do I convert amps to watts?

Multiply volts by amps for a resistive load. For three phase, multiply by √3 as well. Then multiply by power factor for real power.

How many watts is 20 amps?

At 240 V single phase with unity power factor, 4,800 W. At 120 V it is 2,400 W — voltage matters as much as current.

Why does power factor reduce watts?

Because some current flows without doing useful work. The conductors still carry it, which is why cables and breakers are sized on amps rather than watts.

What is the difference between watts and VA?

Watts is real power doing work; volt-amps is apparent power the circuit carries. Power factor is the ratio, and they are equal only on resistive loads.

Does this work for DC?

Yes — set power factor to 1 and use single phase. DC has no reactance, so watts and volt-amps are identical.

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