kVA to kW calculator
10 kW at a power factor of 0.8 needs 12.5 kVA. kW is the power doing work and kVA is what the supply has to carry; the gap is the reactive component, 7.5 kVAR here, circulating without doing anything. A generator sized on the kW figure alone is a fifth too small for this load.
The volt-ampere and the watt have the same dimensions and measure different things, so this is not a unit conversion and no fixed factor exists. kW = kVA × power factor, and without the power factor the question has no answer — which is what every converter that returns the same number is quietly assuming.
Definitions checked against IEEE 1459 and NIST SP 811 · How we check
Real power
85 kW
100 kVA of supply delivers 85 kW of work. The other 52.68 kVAR is reactive: it flows out and back every cycle, does nothing, and still has to be carried by the cable and the generator.
- Apparent power
- 100 kVA
- Real power
- 85 kW
- Reactive power
- 52.68 kVAR
- Power factor
- 0.85
- Phase angle
- 31.8°
- Current at 400 V
- 144.3 A
15% of the supply’s capacity is spent carrying current that does no work. That is why a generator is sold in kVA and not kW — it does not know what you will plug into it — and why an industrial tariff charges for a poor power factor.
If you do not know your power factor
Nameplate-order figures, not measurements. The spread is the point: it is why a 5 kVA generator runs a 5 kW heater and struggles with a 3 kW motor.
Why there is no conversion factor
In an alternating circuit the current does not have to peak at the same instant as the voltage. Where it lags — through a motor winding, a transformer, a fluorescent ballast — part of the current flows into the magnetic field and back out again each cycle. It does no work and it still has to be carried.
Apparent power is voltage times current regardless of timing, measured in volt-amperes. Real power is the part in step, measured in watts. Reactive power is the remainder, in VAR. The three form a right triangle — S² = P² + Q² — and the power factor is the cosine of its angle. At a power factor of one the triangle collapses to a line and a VA is a watt; that case is a kettle, and it is the only one.
Questions people actually ask
- How do you convert kVA to kW?
- Multiply by the power factor: kW = kVA × PF. Going back, kVA = kW ÷ PF. There is no fixed factor, which is why a unit converter cannot do this — the answer depends on the load, and 100 kVA is 100 kW into a heater and 85 kW into a motor at 0.85.
- What is the difference between kVA and kW?
- kVA is apparent power — what the cable, the transformer and the generator have to be sized for. kW is real power — what actually becomes work, heat or light. The gap between them is reactive power in kVAR, current that flows out and back every cycle doing nothing but occupying capacity.
- Why are generators rated in kVA rather than kW?
- Because the generator does not know what you will plug into it. Its limit is current and voltage — apparent power — and how much of that becomes useful work is the load’s business. A 100 kVA set delivers 100 kW to a resistive load and 80 kW to one at 0.8, and the winding is equally hot either way.
- What is a typical power factor?
- Purely resistive loads — heaters, kettles, incandescent lamps — are 1. A whole house averages about 0.9. An induction motor at full load is 0.85 and about 0.5 when lightly loaded, which is why a workshop with idling machines has a worse power factor than one working hard.
- Does a poor power factor cost money?
- On a domestic meter, no: household billing measures kWh, which is real power. On an industrial tariff, yes — supply companies charge for kVA demand or levy a penalty below about 0.95, because the reactive current still has to be generated and carried. Capacitor banks exist to correct it for that reason.
- How do I get amps from kVA?
- Single-phase: A = VA ÷ V. Three-phase: A = VA ÷ (√3 × V line-to-line). 100 kVA at 400 V three-phase is 144 A, not 250 — the root of three is the part people leave out, and it makes the answer 42% too high when they do.
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Sources
- NIST Special Publication 811 — the volt-ampere, the watt and the var
- IEEE Std 1459 — definitions for the measurement of electric power quantities
Arithmetic from the standard definitions. Sizing a supply or a generator for a real installation is an engineer’s job, and starting current on a motor can be six times its running figure.