Power Factor Correction Calculator
Calculate the capacitor bank size needed to correct a lagging power factor to a target value.
Find required kVAR and capacitance in microfarads.
What Is Power Factor? Power factor (PF) is the ratio of real power (kW) to apparent power (kVA). It tells you how efficiently your electrical system is using the current being supplied. A power factor of 1.0 means all supplied current does useful work. A power factor of 0.75 means 25% of the current is “wasted” circulating as reactive power.
Why Low Power Factor Is Costly Utilities supply apparent power (kVA), but bill for real power (kW). With low power factor, you draw more current for the same real power output. This means larger cables, transformers, switchgear, and utility infrastructure — all of which you pay for. Many utilities impose a power factor penalty surcharge for large customers with PF below 0.85 or 0.90. Improving power factor directly reduces demand charges and frees up system capacity.
Causes of Low Power Factor Inductive loads are the primary cause: AC induction motors, transformers, welders, and fluorescent lighting. These loads draw current that lags behind voltage by a phase angle θ. The worse the lag, the lower the power factor.
The Correction Principle Capacitors produce reactive power that is 180° opposite in phase to inductive reactive power. Adding capacitors in parallel with the load cancels out a portion of the inductive reactive current. The goal is not to over-correct to a leading power factor — target just below or at unity (1.0).
The Formulas Current reactive power: Q1 = P × tan(arccos(PF1)) Target reactive power: Q2 = P × tan(arccos(PF2)) Required capacitor kVAR: Qc = Q1 − Q2
For the capacitance value: C = (Qc × 1000) / (2π × f × V²) — result in Farads; multiply by 1,000,000 for microfarads. Where V is the line-to-line voltage (or line-to-neutral for single-phase) and f is the system frequency.
Current and Apparent Power Savings Before correction: S1 = P / PF1 (kVA), I1 = S1 × 1000 / (√3 × V) for 3-phase After correction: S2 = P / PF2 (kVA), I2 = S2 × 1000 / (√3 × V) for 3-phase Reduction in apparent power = S1 − S2 Reduction in current = (1 − PF1/PF2) × 100% This directly reduces losses in cables and transformers proportional to I².
Practical Considerations Capacitor banks are available in fixed steps (e.g., 5 kVAR, 10 kVAR, 25 kVAR). Always round UP to the nearest standard size — slight over-correction to unity is acceptable. Automatic power factor correction (APFC) panels switch capacitor steps in and out based on real-time PF measurement. Do not over-correct past unity — a leading power factor can also cause problems (voltage rise, resonance). Capacitors must be rated for the system voltage with a 10–15% safety margin.