Formula Used
Power factor from power: PF = P / S
Power factor from angle: PF = cos θ
Power factor from impedance: PF = R / Z
Apparent power, single phase: S = V × I
Apparent power, three phase: S = √3 × V × I
Reactive power: Q = √(S² − P²)
Correction size: Qc = P × (tan θ₁ − tan θ₂)
How to Use This Calculator
Select the formula method first. Choose auto mode when you are unsure.
Enter the available electrical values. Use real power with apparent power for the simplest calculation.
Use voltage and current when you also know real power or phase angle.
Enter a target power factor to estimate correction size.
Press calculate. The result appears above the form and below the header.
Use CSV or PDF export for records, homework, or project notes.
Example Data Table
| Load |
Real Power |
Apparent Power |
Power Factor |
Phase Angle |
Reactive Power |
| Small motor |
4.5 kW |
5.3 kVA |
0.849 |
31.91° |
2.78 kVAR |
| Workshop load |
18 kW |
20 kVA |
0.900 |
25.84° |
8.72 kVAR |
| Industrial feeder |
75 kW |
93.75 kVA |
0.800 |
36.87° |
56.25 kVAR |
Power Factor Calculation Formula Guide
Power factor shows how well an alternating current circuit uses supplied power. It compares real power, measured in watts, with apparent power, measured in volt amperes. A value near one means the load uses energy well. A lower value means more current is needed for the same useful work.
Why Power Factor Matters
Motors, transformers, lamps, welders, and chargers often draw reactive current. This current supports magnetic or electric fields. It does not perform useful work, yet it still flows through wires. Extra current can heat conductors, increase voltage drop, and raise equipment size. Utilities may also apply penalties when large facilities run with poor power factor.
Main Formula Idea
The basic relation is PF = P ÷ S. Here P is real power, and S is apparent power. When voltage and current are known, S = V × I for a single phase circuit. For balanced three phase loads, S = √3 × V × I. If the phase angle is known, PF = cos θ. The angle also helps classify the load. A lagging value usually indicates inductive load. A leading value usually indicates capacitive load.
Reactive Power and Correction
Reactive power is found with Q = √(S² − P²). It is measured in var or kilovar. Correction aims to reduce reactive demand. For a target power factor, the needed correction is kvar = P × (tan θ₁ − tan θ₂). The first angle belongs to the current condition. The second angle belongs to the target condition. Capacitor banks are often used for lagging loads. They should be selected carefully for harmonics, duty cycle, and switching steps.
Practical Use
This calculator helps compare several common formulas. It accepts power, voltage, current, angle, resistance, impedance, frequency, and target power factor. The result gives real, apparent, and reactive values. It also gives correction size, current change, and efficiency notes. Use the result for study, early design checks, and report tables. For final installation, follow local electrical codes and measured site data.
Reading the Output
A high result does not always mean low energy cost. It means current is used more effectively. Review voltage, load balance, and duty time too. Record assumptions with every calculation. Small changes in target factor can change correction size greatly during final design review.
FAQs
What is power factor?
Power factor is the ratio of real power to apparent power. It shows how effectively a circuit converts supplied electrical power into useful work.
What is a good power factor?
A power factor near 1 is best. Many systems aim for 0.95 or higher. The required value depends on load type and utility rules.
Can power factor be greater than 1?
No. A valid power factor ranges from 0 to 1. Values above 1 usually mean power, voltage, or current entries are wrong.
What does lagging power factor mean?
Lagging power factor means current lags voltage. It commonly happens with inductive loads, such as motors, transformers, and magnetic ballasts.
What does leading power factor mean?
Leading power factor means current leads voltage. It usually appears when a circuit has too much capacitive effect or overcorrection.
How is reactive power calculated?
Reactive power is calculated as Q = √(S² − P²). It is measured in VAR, kVAR, or MVAR, depending on system size.
Does power factor equal efficiency?
No. Power factor and efficiency are different. Power factor describes current usage. Efficiency compares useful output energy with input energy.
Why add capacitor correction?
Capacitor correction reduces lagging reactive demand. It can lower current, improve voltage regulation, and reduce utility penalties in many installations.