Generator Power Calculator

Your details

Three-phase adds a sqrt(3) = 1.732 factor to all AC formulas. DC has no reactive power or power factor.
Pick what you want to find. Fill in the other fields and this result is calculated.
Line voltage for single-phase; line-to-line voltage for three-phase.
V
Full-load current drawn by the load.
A
Ratio of real power to apparent power (0 to 1). Resistive loads are 1.0; motors are typically 0.7-0.9.
Electrical-to-mechanical efficiency of the motor.
%
Real powerAcceptable power factor
3,840W

Active / real power consumed by the load

Kilowatts3.84kW
Apparent power4.8kVA
Voltage240V
Current20A
Power factor0.8
Horsepower5HP
Real power (kW)3.84
Apparent power (kVA)4.8

Load is 3.84 kW real power.

  • For reliable operation, size the generator to at least 5.8 kVA (20 % headroom above the 4.8 kVA load).
  • Power factor 0.80 means 3.84 kW of real work plus 2.88 kVAR of reactive power. Capacitor banks can improve this.
  • At 240 V the circuit carries 20.0 A. Use a circuit breaker rated at least 25 A (NEC 125 % rule for continuous loads).

Next stepAlways confirm the generator nameplate kVA at the site power factor (usually 0.8). Add starting-surge allowance (2-6x running watts) for motors and compressors.

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