Power Factor Correction Calculator

Enter your load in kW, your current power factor and the target power factor. The calculator works out the capacitor bank size (kVAR) needed to reach the target and shows the reduction in apparent power (kVA).

Many utilities require 0.90 or higher. A common target is 0.95.

How It Works

The power factor correction formula

Power factor (PF) is the ratio of real power (kW) to apparent power (kVA). A load with a low PF draws more current than one with a PF of 1.0 for the same real power. Adding capacitors supplies reactive power locally, reducing the reactive demand on the supply.

The required capacitor reactive power in kVAR is:

Qc = P × (tan(φ1) − tan(φ2))

where P is the real power in kW, φ1 = arccos(PFcurrent) and φ2 = arccos(PFtarget).

Worked example

A 100 kW load has a current power factor of 0.70 and needs correcting to 0.95.

  • tan(arccos 0.70) ≈ 1.0202
  • tan(arccos 0.95) ≈ 0.3287
  • Qc = 100 × (1.0202 − 0.3287) ≈ 69.15 kVAR
  • kVA before = 100 / 0.70 ≈ 142.86 kVA
  • kVA after = 100 / 0.95 ≈ 105.26 kVA
  • Saving ≈ 37.6 kVA of apparent power

A standard capacitor bank is specified in kVAR. Round up to the nearest available bank size and verify with your electrical engineer before installation.

Power Triangle Reference

Real power (kW)

The power actually converted to work or heat. Measured with a wattmeter.

Reactive power (kVAR)

Power stored and returned by inductors and capacitors each cycle. Increases current draw but does no useful work.

Apparent power (kVA)

The vector sum of kW and kVAR: S = √(P² + Q²). Determines cable and transformer sizing.

Frequently Asked Questions

Why should I correct power factor?

A low power factor means you are drawing more current from the supply than the real power alone requires. Utilities often charge a power factor penalty when PF falls below a threshold (commonly 0.85 or 0.90). Correcting it reduces your kVA demand, lowers current in cables and switchgear, cuts I²R losses, and can defer the need for larger transformers or feeders.

How much kVAR do I need to add?

Use the formula Qc = P × (tan φ1 − tan φ2), where P is your real load in kW and the angles are the arccosines of the current and target power factors. The calculator above does this automatically. Round up to the nearest commercially available capacitor bank rating.

What capacitor size do I buy?

Capacitor banks are rated in kVAR at a specific voltage (for example 25 kVAR at 415 V). Select a bank rated at or just above the calculated kVAR, matched to your system voltage. Fixed banks suit steady loads; automatic switching banks (APFCs) work better for variable loads. Always consult a qualified electrical engineer before installation.

What is the kVA reduction benefit?

When apparent power (kVA) drops, so does current for the same real load. This reduces voltage drop along cables, lowers losses, and may push you below a utility demand-charge threshold. In the worked example above, correcting from 0.70 to 0.95 saves about 37.6 kVA, a 26% reduction in apparent power.

What causes a low power factor?

Inductive loads are the main cause: motors, transformers, fluorescent lighting with magnetic ballasts, and welding equipment all draw lagging reactive current. Variable-speed drives and switch-mode power supplies can also cause a low displacement or total power factor. Capacitors add leading reactive current to cancel the lagging component.

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