Amps to kW Calculator

This amps to kW calculator converts electric current into real power for single-phase, three-phase and DC circuits. Enter the current in amps, the voltage, the circuit type and the power factor. You get kilowatts, watts, apparent power in kVA, and the continuous load the breaker can carry.

How to convert amps to kilowatts

Current alone does not tell you power. You also need the voltage, and for AC loads, the power factor (PF), the ratio of real power to apparent power as defined in IEEE Std 1459-2010:

• Single-phase AC or DC: kW = A × V × PF ÷ 1,000
• Three-phase AC: kW = √3 × A × V × PF ÷ 1,000, where V is line-to-line voltage and √3 ≈ 1.732
• Apparent power: kVA = kW ÷ PF
• Continuous breaker load: 80% of the circuit’s kW capacity

For DC circuits there is no power factor, so leave it at 1.

Worked example with the default values

1. Current 30 A, voltage 240 V, single phase, PF 1
2. Real power: 30 × 240 × 1 ÷ 1,000 = 7.2 kW (7,200 W)
3. Apparent power: 7.2 ÷ 1 = 7.2 kVA
4. Continuous load limit at 80%: 7.2 × 0.8 = 5.76 kW

Switch to three-phase at 480 V and the same 30 A gives 1.732 × 30 × 480 ÷ 1,000 = 24.9 kW.

Amps to kW conversion table (PF = 1)

For a power factor below 1, multiply the table value by the PF. A 30 A, 240 V motor at PF 0.85 delivers 7.2 × 0.85 = 6.12 kW.

Amps vs kW: what’s the difference?

Amps measure current, the rate at which electric charge flows; kilowatts measure power, the rate at which energy is used. Voltage links them: the same 30 A is 3.6 kW at 120 V but 7.2 kW at 240 V. Breakers and wires are rated in amps because conductor heating depends on current, while appliances and bills use kW and kWh. To turn kW into energy over time, multiply by hours to get kWh.

Converting kW back to amps

Rearrange the formula: amps = kW × 1,000 ÷ (V × PF) for single-phase, and divide again by 1.732 for three-phase. A 7.2 kW Level 2 EV charger on 240 V draws 30 A. Use the kW to amps calculator to go the other way, with a conversion table and the next standard breaker size for continuous loads under the National Electrical Code.

What affects the result

• Voltage. US homes have 120 V and 240 V circuits; commercial buildings often use 208 V or 480 V three-phase. Measured voltage can sit a few percent above or below nominal.
• Power factor. Heaters, ovens and incandescent lamps are near 1. Motors, compressors and some LED drivers are lower; the DOE notes motor power factor falls at light load.
• Line vs phase voltage. The three-phase formula above uses line-to-line voltage. If you only know phase-to-neutral voltage, multiply amps × volts × PF × 3 instead.
• Starting current. Motors draw several times their running current for a moment at startup; size breakers for that, not just running kW.

Once you know the kW, use the kW to watts converter for other units, or the electricity cost calculator to see what running the load costs. To size backup power for a load, try the UPS calculator. The guide what is a kilowatt-hour explains how kW of power become kWh on your bill.

History of the ampere and three-phase power

The ampere honours André-Marie Ampère, whose work on electrodynamics in the 1820s founded the science of electric current. An international convention at the 1881 International Exposition of Electricity in Paris established the ampere as a standard unit, and since the 2019 SI revision it is defined by fixing the elementary charge (Ampere; NIST SP 330). The three-phase formula in this calculator comes from the polyphase systems of the late 1880s. Nikola Tesla’s US Patent 381,968 for an electro-magnetic motor was granted on 1 May 1888, and Mikhail Dolivo-Dobrovolsky at AEG developed a three-phase generator and motor in 1888. In 1891 he transmitted three-phase power about 176 km from Lauffen to the International Electro-Technical Exhibition in Frankfurt (Dolivo-Dobrovolsky), the demonstration that set three-phase on the way to becoming the standard for grids and industry.

References

• IEEE Std 1459-2010. “IEEE Standard Definitions for the Measurement of Electric Power Quantities Under Sinusoidal, Nonsinusoidal, Balanced, or Unbalanced Conditions.” doi:10.1109/IEEESTD.2010.5439063
• U.S. Department of Energy. Determining Electric Motor Load and Efficiency (fact sheet). energy.gov
• Newell, D. B. & Tiesinga, E. (eds.) (2019). The International System of Units (SI). NIST Special Publication 330. doi:10.6028/NIST.SP.330-2019

Single-phase vs three-phase in plain terms

Single-phase power uses one alternating voltage and is what almost all US homes receive, split into 120 V and 240 V circuits. Three-phase power uses three voltages offset in time, which delivers more power through the same size of wire. That is why factories, large commercial buildings, big heat pumps and many solar inverters above residential size use it. If your panel has three hot bus bars, you have three-phase service.