Understanding Generator Power Ratings (KVA, KW, KVAR, Standby, Prime Power)
A simple explanation of generator rating terminology and why generators are labeled the way they are.
Generators are traditionally labeled using kVA (kilovolt-amps) even though most jobsite needs are measured in kW (kilowatts). kVA represents apparent power, which includes both real usable power (kW) and reactive power (kVAR). In a perfect system, kW would equal kVA, but in real applications only about 80 percent of the kVA rating becomes usable output.
This kVA labeling standard began as a marketing practice because a kVA value appears larger than a kW value for the same generator. The industry continued using this approach, so most generators today still display kVA ratings even though customers size equipment in kW.
kVAR refers to reactive power, or the portion of total power that does not convert into useful work. Real work such as light, heat, motion, and sound is produced by kW. One kilowatt equals 1,000 watts, and watts can be converted to kW by dividing by 1,000.
Understanding generator ratings also requires knowing the difference between Standby and Prime Power units. A Standby generator runs only during power outages and typically operates 250 hours per year. A Prime Power generator serves as the primary power source for long-term or continuous use. Prime units run 6,000–8,000 hours per year and support variable loads. This is the rating used for mobile and rental applications.
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