Utility July 13, 2026 · 8 Min Read

Power Factor Calculator – Guide & Formulas

Calculate real, reactive, and apparent power, and size capacitor banks (kVAR) to optimize AC system power factor levels.

Optimize electrical transmission efficiency. Input active load power, initial power factor, and desired target power factor to determine the necessary reactive capacitor rating (kVAR) to eliminate voltage lags.

Key Takeaway

Use the free Power Factor Calculator to calculate real, reactive, and apparent power, and size capacitor banks (kvar) to optimize ac system power factor levels. Get instant results with step-by-step explanations.

How to Use the Power Factor Calculator

  1. Enter the active system load measured in Kilowatts (kW).
  2. Input the current operating power factor (usually lagging, between 0.50 and 0.90).
  3. Input your targeted power factor (e.g., 0.95 or 0.98).
  4. Review the required capacitor size in kVAR alongside apparent power changes.

The Formula

Required Capacitor (kVAR) = Active Power * (tan(arccos(Current PF)) - tan(arccos(Target PF)))

Variable Definitions

  • P: Active circuit load power measured in Kilowatts (kW)
  • Q_cap: Required capacitive reactive power correction in kVAR
  • theta_1 / theta_2: Phase angles associated with the initial and corrected power factors

Correcting a 150 kW Load to 0.95 PF

Determine capacitor size for a 150 kW load running at 0.75 PF lagging, with a target of 0.95 PF.

  1. Step 1: Compute initial phase angle: arccos(0.75) ≈ 41.41° -> tan(41.41°) ≈ 0.8819.
  2. Step 2: Compute target phase angle: arccos(0.95) ≈ 18.19° -> tan(18.19°) ≈ 0.3287.
  3. Step 3: Solve difference: 0.8819 - 0.3287 = 0.5532.
  4. Step 4: Solve capacitor bank requirement: 150 kW × 0.5532 ≈ 83.0 kVAR.

Frequently Asked Questions

What is power factor?

Power factor is the ratio of real active power (kW) performing useful work, divided by apparent total power (kVA) supplied to the circuit.

What causes low power factor?

Lagging power factor is caused by inductive loads like electric motors, transformers, and fluorescent lighting ballasts that create lag between AC voltage and current waveforms.