How To Size Your Generator Correctly (KVA To KW To Single-Phase Output)
A simple breakdown of how real generator output is calculated and how single-phase operation reduces available power.
A generator labeled as 25 kVA does not provide 25 kW of usable power. In most cases, real output equals 80 percent of the kVA rating. That means a 25 kVA generator supplies about 20 kW in three-phase operation. This relationship is true for generators of any size.
If the generator is switched into single-phase, output drops further. The voltage selector reconfigures the internal windings so that only two of the three output lines provide power. As a result, available kW decreases by roughly one-third. For example, a generator offering 20 kW in three-phase delivers only about 14 kW in single-phase.
These reductions should always be considered when selecting a generator for your jobsite. The model number reflects the kVA rating, but actual available power is always lower, especially when operating in single-phase.
Accurate sizing ensures the generator runs within its optimal load range and helps prevent mechanical and emissions-related issues. Understanding these differences helps you avoid misapplication and ensures your generator is properly matched to your load.