Watts to Amps to Volts Calculator

Enter any two of power, voltage and current, choose the system and power factor, and this calculator works out the third using P = V × I (with the power factor and √3 factor for AC).

System

Power (W)

Voltage (V)

Current (A)

Fill exactly two of W, V, A.

How It Works

Power relations

DC: P = V × I
Single-phase AC: P = V × I × PF
Three-phase AC: P = √3 × V × I × PF

For three-phase, V is the line-to-line voltage. Power factor (PF) is the ratio of real power to apparent power and is 1 for a purely resistive load.

Worked example

A single-phase load at 120 V drawing 10 A with a power factor of 0.8: P = 120 × 10 × 0.8 = 960 W.

Frequently Asked Questions

How do I convert watts to amps?

Divide power by voltage (and by the power factor for AC): amps = watts / (volts times power factor). For three-phase, also divide by the square root of 3.

How do I convert amps to watts?

Multiply voltage by current (and by the power factor for AC): watts = volts times amps times power factor. For three-phase, also multiply by the square root of 3.

What is power factor?

Power factor is the ratio of real power (watts) to apparent power (volt-amps). It is 1 for resistive loads and less than 1 for motors and other reactive loads.

Why is three-phase multiplied by the square root of 3?

In a balanced three-phase system the total power from line-to-line voltage and line current works out to the square root of 3 times the single-phase product.

Do I use line-to-line or line-to-neutral voltage?

This calculator uses line-to-line voltage for three-phase, which is the standard way three-phase supplies are quoted.

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