Amps to kW Calculator (Three-Phase and Single-Phase)
Convert measured line current to real power, or size the expected current from a known kW load. Unlike the kVA conversion, this one needs power factor — that is what separates the power actually doing work from the power merely moving through the conductor.
Power factor drives this result directly. Estimating 0.85 when the true value is 0.65 overstates real power by about 30%. If the number feeds a billing dispute, a generator sizing, or a capital request, measure it — do not assume it.
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A free calculator gets you in the ballpark. For permit-stamped, defensible work, ClarkTE delivers a PE-stamped load study and power factor analysis from a working engineer, based on your one-line and load data.
kW, kVA, and kVAR: what the three numbers mean
Every AC load draws current in two components. One is in phase with the voltage and does actual work — that is real power, measured in kW. The other lags or leads, sustaining magnetic fields in motors and transformers without performing work — that is reactive power, in kVAR. The vector sum is apparent power, in kVA, and it is what your conductors and transformers actually have to carry.
Power factor is the ratio: pf = kW ÷ kVA. At a power factor of 0.65, a 100 kW load pulls 154 kVA through the system — you are paying for conductor and transformer capacity that produces nothing.
Worked examples
- 100 A at 480 V three-phase, pf 0.85: (1.732 × 480 × 100 × 0.85) ÷ 1000 = 70.7 kW (83.1 kVA)
- 50 A at 240 V single-phase, pf 1.0: (240 × 50 × 1.0) ÷ 1000 = 12.0 kW
- 200 A at 208 V three-phase, pf 0.80: (1.732 × 208 × 200 × 0.80) ÷ 1000 = 57.6 kW (72.1 kVA)
Amps to kW: frequently asked questions
How do you convert amps to kW on a three-phase system?
kW = (√3 × V × I × pf) / 1000. A 480 V three-phase load drawing 100 A at 0.85 power factor is (1.732 × 480 × 100 × 0.85) / 1000 = 70.7 kW.
Why does converting amps to kW need power factor when kVA does not?
kW is real power — the portion actually doing work. kVA is apparent power, the raw product of volts and amps. The ratio between them is power factor, so kW = kVA × pf. Converting current to kVA needs only voltage; converting to kW additionally needs pf.
What power factor should I assume if I do not know it?
Do not assume if you can measure. Where you must estimate: induction motors at full load typically run 0.80 to 0.88, lightly loaded motors drop well below 0.70, resistive heating is 1.0, and modern switch-mode electronics with power factor correction are usually above 0.95. A wrong pf assumption scales the answer proportionally.
Is kW the same as kWh?
No. kW is the instantaneous rate of energy use; kWh is the quantity consumed over time. A 70 kW load running for three hours consumes 210 kWh. Utility demand charges bill kW, energy charges bill kWh.
Does this apply to motor nameplate horsepower?
Only indirectly. Nameplate horsepower is mechanical output power; kW here is electrical input power. Input kW = (hp × 0.746) / efficiency. A 100 hp motor at 94% efficiency draws roughly 79 kW electrical, not 74.6 kW.
Want to do this for a living?
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