AC power & power factor calculator
Real, reactive, and apparent power — single and three phase — plus PF correction sizing and efficiency.
How it works
The power triangle: apparent power S = V×I is the hypotenuse, real power P = S·cosφ does the work, reactive power Q = √(S²−P²) sloshes between the source and the load's fields. Power factor is just cos φ — the fraction of the current that's actually working. Correction adds the opposite reactance so the sloshing happens locally in the capacitor instead of through every wire upstream: Q_C = P(tanφ₁ − tanφ₂), C = Q_C/(2πfV²).
Common questions
Because the CURRENT that carries it is real: it heats wires, fills transformer capacity, and trips breakers exactly like working current. A 0.7-PF load draws ~43% more current than a unity-PF load doing the same work — that's why utilities bill industry for poor PF, and why your wiring is sized in kVA, not kW.
Line-to-line voltage versus phase voltage. Three 120°-shifted phases mean V_LL = √3 × V_LN, and the power algebra inherits it: P = √3 × V_LL × I_L × PF. Use line-to-line voltage with line current and the √3 form is always self-consistent for balanced loads.
It must be sized for THIS load at THIS operating point — an oversized cap over-corrects into a leading PF, which is its own problem. Motors that vary load (compressors) often need switched banks. And the cap sees full line voltage forever: use proper X2/motor-run rated parts, never generic electrolytics.