Electrician Prep

Amps to kW Calculator

Convert amps to kilowatts instantly. Free calculator for single-phase and three-phase electrical circuits.

About this calculator

Amps and kilowatts are not interchangeable - amps is current, kilowatts is power - but the conversion is one of the most common quick calculations on the job. You need voltage and (for non-resistive loads) power factor to bridge between them. This converter handles single-phase and three-phase circuits with adjustable PF.

Formula

For DC and resistive single-phase loads, kW equals volts times amps divided by 1000. AC single-phase with reactive components multiplies by power factor. Three-phase adds the √3 multiplier.

Single-phase: kW = (V × I × PF) ÷ 1000
Three-phase: kW = (√3 × V × I × PF) ÷ 1000

How to use

  1. Pick single-phase or three-phase.
  2. Enter the current in amps and the system voltage.
  3. Enter the power factor (1.0 for resistive heaters, 0.85-0.9 for motors).
  4. Read the result in kilowatts.

Worked example

Setup

A single-phase 240 V resistive water heater draws 21 A. Convert to kW.

Calculation

kW = (240 × 21 × 1.0) ÷ 1000 = 5,040 ÷ 1000 = 5.04 kW.

Answer

The water heater consumes 5.04 kW. Resistive loads have a power factor of 1.0, so kW equals kVA in this case.

Frequently asked questions

What power factor should I use?
For purely resistive loads (water heaters, electric heat, incandescent lamps): 1.0. For typical motor loads under load: 0.80 to 0.90. For LED drivers and electronic ballasts: check the nameplate, often 0.90 or better. When in doubt and the load is not nameplate-marked, 0.85 is a common estimate.
Is this kW or kVA?
kW is real power - what your meter bills you for. kVA is apparent power - what determines wire and breaker sizing. The two are related by power factor: kW = kVA × PF. This calculator outputs kW.
Why does the answer change for three-phase?
Three-phase systems deliver power across three phase conductors instead of one, with a √3 multiplier in the power equation. The same line-to-line voltage and line current produce more total power on three-phase than on single-phase.