AC loads split into real kilowatts and reactive kVAR—power factor links them to apparent kVA. This guide walks through the power factor and reactive power calculator: kVA, PF as a decimal, and the reactive component your breakers still see.
Benefits
- kW = kVA × power factor; kVAR = √(kVA² − kW²).
- Outputs kW, kVAR, kVA, PF, and phase angle φ together.
- Motor PF often 0.7–0.9; resistive loads near 1.0.
How it works
- Enter apparent power in kVA from equipment plate or load study.
- Add power factor (0–1)—measured or typical for motor vs. resistive mix.
- Read reactive kVAR plus real kW—size on kVA, budget on kW.
FAQ
How do I calculate reactive power from power factor?
kW = kVA × PF, then kVAR = √(kVA² − kW²). Example: 12 kVA at 0.85 PF → kW = 10.2 → kVAR = √(144 − 104.04) ≈ 6.32 kVAR. Lower PF means more kVAR for the same kVA.
What is the difference between kW, kVAR, and kVA?
kW is real power (useful work). kVAR is reactive power (magnetizing/inductive exchange). kVA is apparent power—the vector sum: kVA² = kW² + kVAR². Conductors and transformers are limited by kVA and current, not kW alone.
Why does poor power factor matter for inverters?
An inverter rated in kVA must supply both kW and kVAR demanded by the load. A 10 kW motor at 0.75 PF may need ~13.3 kVA apparent—exceeding a 10 kVA inverter even though real power fits. Calculate kVAR before assuming wattage equals sizing.
Technical specifications
- kW = kVA × PF.
- kVAR = √(kVA² − kW²).
- PF = kW ÷ kVA; φ = arccos(PF).
- Related: kva-to-kw, inverter-sizing, amps-to-watts.
The power triangle in one tool
Apparent kVA is the hypotenuse; real kW and reactive kVAR are the legs. Power factor is how much of kVA lands in kW—unity PF is all real; 0.8 PF leaves a significant kVAR leg. Entering kVA and PF recreates the full triangle so you do not size feeders on kW alone while current follows kVA.
Motors and VFDs dominate kVAR
Induction motors, compressors, and some LED drivers present lagging power factor. A workshop with several motors may show 0.75–0.85 PF site-wide. Reactive power calculator output explains why a 15 kVA service feels tight at only 11 kW of useful load—the remaining apparent capacity is tied in reactive exchange, not wasted heat, but still counts toward ampacity.
From kVAR to procurement
Use calculated kVAR in BOM notes alongside kVA for gensets, UPS, and off-grid inverters. If kVAR is large, consider power-factor correction capacitors or higher kVA gear. Pair results with kVA to kW Converter when vendors quote only one of the three numbers—never assume they are interchangeable without PF.