How do I calculate the capacitor size for power factor correction?

Calculate the required kVAR using: kVAR = P × (tan(acos(PF1)) - tan(acos(PF2))), where P is real power in kW, PF1 is existing PF, and PF2 is target PF. Then convert to microfarads using: C = (kVAR × 10⁹) / (2π × f × V²).

What is a good power factor value?

A power factor of 1.0 (unity) is ideal, meaning all power is used for useful work. Values above 0.95 are considered excellent, 0.90 to 0.95 is good, 0.80 to 0.90 is fair, and below 0.80 is poor. Most utilities require PF above 0.90 to avoid penalties.

Power Factor Calculator

Calculate power factor, reactive power, apparent power, and capacitor size for PF correction. Includes an interactive power triangle visualization.

Real Power (kW)

Apparent Power (kVA)

Existing Power Factor

Target Power Factor

Real Power (kW)

Frequency

System Voltage (V)

Power Factor

—

Cos φ

Phase Angle

—

Degrees

Reactive Power

—

kVAR

Capacitor Size

—

µF

How to Use the Power Factor Calculator

Compute power factor and correction in three simple steps.

Choose Mode

Select 'PF Calculator' to compute PF from real and apparent power. Select 'PF Correction' to determine capacitor size needed to improve your power factor.

Enter Parameters

For PF mode, enter kW and kVA. For correction mode, enter existing and target PF, real power, frequency, and system voltage.

Review Results

View power factor, phase angle, reactive power, and the dynamic power triangle. Correction mode also shows required capacitor size in microfarads.

Frequently Asked Questions

Common questions about power factor and correction.

Power factor (PF) is the ratio of real power (kW) to apparent power (kVA). A low PF means your electrical system is inefficient, drawing more current than necessary. Utilities often charge penalties for PF below 0.9. Improving PF reduces energy costs and frees up system capacity.

Calculate required kVAR using: kVAR = P × (tan(acos(PF1)) - tan(acos(PF2))). Then convert to microfarads: C = (kVAR × 10⁹) / (2π × f × V²). Our calculator does both steps automatically.

PF of 1.0 is ideal. Above 0.95 is excellent, 0.90-0.95 is good, 0.80-0.90 is fair, and below 0.80 is poor. Most utilities require PF above 0.90 to avoid penalties.

Common causes include induction motors running at less than full load, transformers, arc welders, induction furnaces, and lighting ballasts. These inductive loads draw reactive power that lowers the power factor.

The power triangle shows the relationship between real power P (kW) on the horizontal axis, reactive power Q (kVAR) on the vertical axis, and apparent power S (kVA) as the hypotenuse. The angle between S and P is the phase angle θ, where PF = cos(θ).