kVA vs kW: Apparent Power, Real Working Power & Power Factor Sizing
kVA (kilovolt-amperes) represents total apparent electrical power supplied to an AC circuit, whereas kW (kilowatts) measures actual working power converted into heat, light, or shaft rotation. The ratio between real power and apparent power is the Power Factor (PF = kW / kVA), which ranges from 0.0 to 1.0 (typically 0.80 in industrial motor and commercial generator applications).
Technical Comparison & Conversion Matrix
| Parameter | kVA (Kilovolt-Amperes) | kW (Kilowatts) |
|---|---|---|
| Physical Dimension | Apparent Power (S) | Real / Active Working Power (P) |
| Vector Mathematics | S = V * I (Hypotenuse of Power Triangle) | P = V * I * cos(theta) (Adjacent Leg) |
| Inductive Load Phase | Includes reactive power (kVAR) magnetizing coils | Excludes reactive power losses |
| Equipment Sizing | Transformers, UPS systems, alternators, utility feeds | Electric motors, heaters, compressors, server loads |
| Standard Power Factor | 100 kVA generator @ 0.80 PF = 80 kW engine capacity | 80 kW demand / 0.80 PF = 100 kVA service capacity |
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Frequently Asked Questions
Why are commercial generators and transformers rated in kVA rather than kW?
Manufacturers cannot predict the inductive power factor of the end user's loads. Since conductors and transformer windings overheat based on total current (amperes), kVA indicates the thermal current-carrying limit regardless of power factor.
Can kW ever exceed kVA in an AC circuit?
No. Under Euclidean power triangle geometry (kVA^2 = kW^2 + kVAR^2), real power (kW) can only be less than or equal to apparent power (kVA). The maximum theoretical equality occurs at unity power factor (PF = 1.00) in purely resistive loads.