What is the Generator Power Calculator?
This calculator converts the electrical values measured at a generator's terminals — voltage, current and power factor — into useful power ratings: real power in kilowatts (kW), apparent power in kilovolt-amperes (kVA) and mechanical equivalent in horsepower (hp). It supports both single-phase and balanced three-phase systems, making it handy for sizing standby generators, portable units and industrial gensets.
How to Use It
Select whether your generator is single-phase or three-phase. Enter the line voltage (V), the current draw (A) and the power factor (PF, typically 0.8 for generators). The tool instantly returns the real power, apparent power and horsepower. Use kVA when sizing the alternator, kW when matching the engine and load.
The Formula Explained
For a three-phase system, real power is $$P(\text{kW}) = \dfrac{V \times I \times \text{PF} \times \sqrt{3}}{1000}$$. The \(\sqrt{3}\) (≈1.732) factor accounts for the phase relationship between the three lines. For single-phase, simply $$P(\text{kW}) = \dfrac{V \times I \times \text{PF}}{1000}$$. Apparent power (kVA) uses the same expression without the power factor, since \(\text{kVA} = \text{kW} \div \text{PF}\). Horsepower is found by multiplying kW by \(1.34102\).
Worked Example
A three-phase generator delivers 400 V at 100 A with a power factor of 0.8. Apparent power $$= \dfrac{400 \times 100 \times 1.732}{1000} \approx 69.28 \text{ kVA}.$$ Real power $$= 69.28 \times 0.8 \approx 55.43 \text{ kW}.$$ In horsepower, \(55.43 \times 1.34102 \approx 74.32 \text{ hp}\).
FAQ
What power factor should I use? Most generators are rated at 0.8 PF. Resistive loads (heaters) approach 1.0, while motors are lower.
Is the voltage line-to-line? For three-phase, use the line-to-line voltage (e.g. 400 V or 480 V).
kW or kVA for sizing? Engine output is rated in kW, alternator capacity in kVA. Size to the larger requirement of your load.
