kVA to kW Converter (and kW to kVA)

The Power Triangle AC electrical systems have three kinds of power, and they form a right triangle rather than adding up: Real Power (P, in kW): the power actually converted to useful work, whether that is heat, light or motion. Apparent Power (S, in kVA): the total the source has to supply, and what the utility bills for in large installations. Reactive Power (Q, in kVAR): power that sloshes back and forth into inductive and capacitive loads such as motors and transformers, doing no useful work on the way.

The geometry is the whole point. A load drawing 80 kW and 60 kVAR needs 100 kVA from the supply, not 140, because S = √(P² + Q²). Adding the two straight together is the single most common mistake in generator sizing.

The Power Factor Power Factor (PF) = kW / kVA = cos(θ) Where θ is the phase angle between voltage and current. PF = 1.0 (unity): current and voltage are in phase, a purely resistive load such as a heater or an incandescent bulb. PF = 0.8 (common for motors): current lags voltage, so more apparent power is needed for the same real work. PF = 0.9 and above: typical of modern efficient equipment and of installations with correction fitted.

The Formulas kW = kVA × PF kVA = kW / PF kVAR = √(kVA² − kW²) PF = kW / kVA = cos(arctan(kVAR / kW))

Why kVA Matters Generators are rated in kVA because they provide apparent power, not just real power. A 100 kVA generator can supply 80 kW of real power at 0.80 PF. UPS (Uninterruptible Power Supply) systems are sized in kVA. A 10 kVA UPS at 0.9 PF can power 9 kW of actual equipment. Transformers are also rated in kVA because they are affected by both real and reactive components.

Power Factor Correction Poor power factor is expensive, because utilities levy demand charges on installations that draw a lot of apparent power for little real work. Power factor below 0.85 often triggers a surcharge. Capacitor banks are added to correct power factor toward unity by offsetting inductive reactive power. Modern variable frequency drives (VFDs) include built-in power factor correction.

Common Power Factors by Equipment Type Resistive loads (heaters, toasters): PF = 1.0. Incandescent lighting: PF = 1.0. Fluorescent lighting (electronic ballast): PF = 0.95–0.99. AC induction motors (unloaded): PF = 0.3–0.5. At full load: PF = 0.85–0.92. Computers and electronic equipment: PF = 0.6–0.7 (without PFC) or 0.95–0.99 (with active PFC). Welding equipment: PF = 0.35–0.60.

Generator and UPS Sizing Rule of Thumb For motors and mixed loads: add 25% margin above calculated kVA for startup surges. For critical IT infrastructure: size UPS at 150% of actual kW load at 0.9 PF. Standby generators should be sized at 100–125% of site peak demand in kVA.