kVA to kW Calculator
Enter apparent power in kVA and power factor to get real power in kilowatts and reactive power in kVAR — the values you need to size generators, UPS units, and electrical systems correctly.
Generators and UPS units are rated in kVA
Equipment nameplates show kVA because that is the maximum apparent power the device can supply. The kW it can actually deliver to the load depends on the load's power factor.
Power factor varies with load type
Mixed loads — motors, lighting, electronics — shift the power factor away from the nameplate value as load changes. Use the actual measured power factor when sizing critical systems.
What is kVA and how does it differ from kW?
Apparent power, real power, and the power factor relationship
Kilovolt-amperes (kVA) measure apparent power — the total power flowing in an AC circuit regardless of whether it does useful work. Kilowatts (kW) measure real power — the portion that actually performs work such as turning a motor or producing heat. The power factor (PF) is the ratio between them: kW = kVA × PF. A power factor of 1.0 means every volt-ampere is converted to useful work; a power factor below 1.0 means some of the apparent power circulates as reactive power (kVAR) without doing work.
Enter the apparent power in kVA and the power factor to get real power in kW and reactive power in kVAR instantly.
Multiply the apparent power by the power factor to get real power. For reactive power, multiply the apparent power by the sine of the phase angle, which equals the square root of one minus the power factor squared.
kW = kVA × PF kVAR = kVA × √(1 − PF²)At a power factor of 0.8 — typical for many industrial and commercial loads — a 10 kVA generator can deliver only 8 kW of actual working power. A 100 kVA transformer at unity power factor (PF = 1.0) delivers the full 100 kW with zero reactive power. A 50 kVA UPS feeding a data centre with a power factor of 0.9 delivers 45 kW, with approximately 21.8 kVAR of reactive power.
The real power figure (kW) tells you how much useful work the electrical system can perform. When sizing a generator or UPS, always match the kW rating to the actual load demand — not just the kVA rating. If your loads draw 8 kW at a power factor of 0.8, you need a generator rated at least 10 kVA (8 ÷ 0.8 = 10) to avoid overloading the machine. A higher power factor means more of the apparent power becomes useful output: at PF 0.95 a 10 kVA unit delivers 9.5 kW, while at PF 0.7 it delivers only 7 kW. The reactive power figure (kVAR) shows how much power oscillates between the source and the load without doing work; large reactive power values reduce the efficiency of the distribution system and may require power factor correction capacitors to bring the power factor closer to 1.0.
This calculator assumes a single-phase or balanced three-phase load with a known, constant power factor.
Real power factors drift with load and are not always shown on nameplates
The power factor of a motor, compressor, or variable-frequency drive changes with the percentage of full load it is carrying. A motor running at 50 % load typically has a significantly lower power factor than at full load. Generator and UPS nameplates may quote a reference power factor (commonly 0.8 or 0.9) that does not match the actual load. Measure the true power factor with a power analyser for critical sizing decisions, and add a safety margin of at least 20 % to the calculated requirement.