Amps to kW Calculator

About the Amps to kW Calculator

An amps to kW calculator converts electrical current in amperes to real power in kilowatts, an essential conversion for electricians, engineers, homeowners, and anyone sizing generators, circuit breakers, or appliances. Amps (A) measure the rate of electron flow through a conductor; kilowatts (kW) measure the rate of real work being done by that current. The two quantities are related through voltage and power factor — you cannot convert amps to kW without knowing the circuit voltage and the power factor of the load. Our free amps to kW calculator handles both single-phase and three-phase AC circuits, accepts any voltage (120V, 208V, 230V, 240V, 277V, 480V), and uses an adjustable power factor slider. It is widely used by US and Canadian electricians sizing residential 120/240V circuits, UK and Australian engineers working with 230/415V systems, and industrial facilities evaluating 480V three-phase equipment. The reverse calculation — converting kW back to amps — is equally important for circuit breaker selection and is available in our kW to amps calculator.

How It Works

Single-phase formula: kW = (A × V × PF) / 1000. Three-phase formula: kW = (A × V × PF × √3) / 1000, where √3 = 1.732. Variables: A = current in amperes, V = line voltage in volts, PF = power factor (0 to 1, dimensionless). Example 1 (single-phase): 20A circuit at 120V, PF 0.85. kW = (20 × 120 × 0.85) / 1000 = 2,040 / 1,000 = 2.04 kW. Example 2 (3-phase): 30A at 208V, PF 0.9. kW = (30 × 208 × 0.9 × 1.732) / 1000 = 9,730 / 1,000 = 9.73 kW. Power factor for resistive loads (heaters, incandescent bulbs): PF = 1.0. For inductive loads (motors, transformers): PF = 0.7–0.9 typically. Capacitive loads can produce leading power factor above 1 in specialized applications.

Tips & Best Practices

• ✓Always use the correct voltage for your phase configuration: for 3-phase calculations, use line-to-line voltage (208V, 380V, 415V, 480V) — not the line-to-neutral voltage (120V, 230V). Using line-to-neutral voltage in 3-phase formulas produces results that are √3 ≈ 1.73× too low.
• ✓For motors and compressors, use a power factor of 0.7–0.85 when the nameplate does not specify. Fully loaded motors typically operate at PF 0.85–0.90; lightly loaded motors can drop to PF 0.5–0.70. Wrong PF assumptions significantly affect circuit sizing.
• ✓The NEC (National Electrical Code) requires circuit breakers to be sized at 125% of continuous load current. If your calculation shows 20A, the minimum breaker size is 25A; round up to the next standard size (30A).
• ✓LED and switching power supplies often have poor power factor (0.5–0.7) without power factor correction (PFC). LED drivers with built-in PFC achieve PF > 0.9. For lighting loads, check the driver datasheet for actual PF.
• ✓UK and Australian 230V single-phase systems deliver the same kW as US 120V at roughly twice the amperage, all else equal. A 10A circuit at 230V produces 2.3 kW × PF; the same load would draw 19.2A at 120V.

Who Uses This Calculator

Electricians calculating the power demand of a circuit based on measured current. Engineers sizing generators, transformers, and distribution panels. Homeowners evaluating how much load is on a circuit before adding appliances. Facilities managers calculating energy demand for utility billing. Anyone installing EV chargers, solar inverters, or industrial equipment who needs to verify circuit capacity.