Power Factor Calculator
Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer
Last updated: July 27, 2026Why power factor matters
In AC circuits with reactive loads (motors, transformers, fluorescent ballasts), voltage and current can fall out of phase with each other. Power factor measures how much of the apparent power delivered actually does useful work versus circulating uselessly between source and load.
Worked example
For a load drawing 120V at 8A, with 800W of measured real power:
Apparent Power = V x I = 120 x 8 = 960 VA
Power Factor = Real Power / Apparent Power = 800 / 960 = 0.833 (angle: 33.56 deg)
Utility companies often charge industrial and commercial customers a penalty for power factor below about 0.9, since a low power factor means the utility must supply more current than the useful power alone would require - many facilities install capacitor banks specifically to correct power factor closer to 1.0.