Choose a method
Use kW and kVA, kW and kVAR, electrical measurements, or a measured phase angle.
Electrical & Energy Tool
Power Factor Calculator
Calculate AC power factor from kW and kVA, kW and kVAR, voltage and current, or phase angle. Review the complete power triangle and estimate the correction needed to reach a target power factor.
Four calculation methods Single and three phase Correction kVAR estimate
How to use the power factor calculator
Select the method that matches the values available, enter the measurements in compatible units, then review power factor, phase angle, the complete power triangle, and the optional correction estimate.
Enter verified values
Use RMS voltage and current plus real power from reliable nameplate or metering data.
Review PF and correction
Check the formula, phase angle, kVA, kVAR, quality band, and target correction requirement.
Understanding power factor and the power triangle
Power factor is the ratio of useful real power to total apparent power in an AC circuit. A value closer to 1 means more of the supplied current is producing useful work.
Core power factor formulas
From real and apparent power
PF = P ÷ SFrom real and reactive power
PF = P ÷ √(P² + Q²)From phase angle
PF = cos(φ)Correction to a target
Qc = P × [tan(φ1) − tan(φ2)]What P, Q, and S mean
Real power (P), measured in watts or kilowatts, performs useful work. Reactive power (Q), measured in var or kVAR, supports magnetic and electric fields. Apparent power (S), measured in VA or kVA, is the combined electrical demand.
Lagging power factor is commonly associated with motors, transformers, and inductive loads. Leading power factor is commonly associated with capacitive systems or over-correction.
Quick reference examples
| Real power | Apparent / reactive value | Method | Power factor | Phase angle |
|---|---|---|---|---|
| 80 kW | 100 kVA | P ÷ S | 0.800 | 36.87° |
| 90 kW | 43.59 kVAR | P ÷ √(P² + Q²) | 0.900 | 25.84° |
| 95 kW | 100 kVA | P ÷ S | 0.950 | 18.19° |
| 100 kW | 100 kVA | Unity | 1.000 | 0° |
The correction result is an engineering estimate, not a final capacitor-bank design. Switching steps, harmonics, resonance, transformer impedance, load variation, voltage, temperature, discharge requirements, and local standards must be assessed by a qualified electrical professional.
Power factor calculator FAQs
What is a good power factor?
A power factor of 0.90 or higher is commonly considered good, while many facilities aim for 0.95 or better. The appropriate target depends on utility rules, equipment, operating conditions, and site design.
How is power factor calculated from kW and kVA?
Divide real power in kW by apparent power in kVA. For example, 80 kW divided by 100 kVA gives a power factor of 0.80.
What is the difference between leading and lagging power factor?
Lagging power factor means current lags voltage and is typical of inductive loads. Leading power factor means current leads voltage and is typical of capacitive loads or an over-corrected installation.
Can power factor be greater than 1?
No. The magnitude of true power factor ranges from 0 to 1. A calculated value above 1 indicates inconsistent units, incorrect phase selection, or inaccurate measurements.
Does low power factor increase electricity use?
For the same useful kW, low power factor requires more current and kVA. This can increase conductor and transformer losses, reduce available system capacity, and may lead to utility demand charges or penalties.
Can this tool design a capacitor bank?
It estimates the reactive compensation required for a selected target. A final capacitor-bank design requires harmonic, resonance, switching, protection, duty-cycle, and standards checks by a qualified professional.
Electrical safety reminderUse true RMS and real-power measurements from suitable instruments. Final correction equipment and protection settings should be designed and verified by a qualified electrical professional.