Power Factor Correction Calculator
Size the capacitor bank needed to raise power factor to a target value.
About Power Factor Correction Calculator
The capacitor must supply the difference between present and target reactive power. Converting kVAR to capacitance depends on frequency and the square of voltage, so the same kVAR needs far less capacitance at higher voltage. Over-correcting into a leading power factor is also penalised and can cause resonance with harmonics, so correction is normally targeted at about 0.95.
Formula
Power Factor Correction
Q_c = P (tan φ₁ − tan φ₂); C = Q_c ÷ (2π f V²)
- Q_c
- Capacitive reactive power required
- C
- Capacitance needed at the system voltage
Worked example
With the default values below, Power Factor Correction Calculator returns Capacitor Rating Required of 51.062. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Real powerminimum 0 kW
- 100 kW
- Present power factoraccepts 0.01–1
- 0.78
- Target power factoraccepts 0.01–1
- 0.96
- System voltageminimum 1 V
- 400 V
- Annual charge per kVA of capacityminimum 0
- 40
Results
- Capacitor Rating Required
- 51.062 kVAR
- Equivalent Capacitance per Phase
- 1,015.84 uF
- Apparent Power Before
- 128.205 kVA
- Apparent Power After
- 104.167 kVA
- Annual Capacity Charge Saved
- $961.54
Step by step
- 1Values used
- 2Power Factor Correction
- 3Capacitor Rating Required= 51.062 kVAR
- 4Equivalent Capacitance per Phase= 1,015.84 uF
- 5Apparent Power Before= 128.205 kVA
- 6Apparent Power After= 104.167 kVA
- 7Annual Capacity Charge Saved= 961.54
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation or tax into account.
- Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Power Factor Correction calculated?
Q_c = P (tan φ₁ − tan φ₂); C = Q_c ÷ (2π f V²) The capacitor must supply the difference between present and target reactive power. Converting kVAR to capacitance depends on frequency and the square of voltage, so the same kVAR needs far less capacitance at higher voltage.
Why does Power Factor Correction matter?
Over-correcting into a leading power factor is also penalised and can cause resonance with harmonics, so correction is normally targeted at about 0.95.
What values do I need to enter?
This calculator takes 5 inputs: Real power, Present power factor, Target power factor, System voltage, Annual charge per kVA of capacity. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.