Power Factor Calculator
This power factor calculator solves the full AC power triangle from any two known values — enter any two of real power (P), reactive power (Q), apparent power (S), power factor (PF), or phase angle (φ) and it computes the rest instantly. It's built for electricians, electrical engineers, and students working with motors, transformers, and industrial loads.
Power factor is the ratio of real power to apparent power (PF = P / S = cos φ), and it measures how efficiently a circuit uses the power it draws. Alongside the numbers, the tool draws the power triangle, rates your PF, and sizes the capacitor bank you need for power factor correction.
How to Use the Power Factor Calculator
Enter any two values
Type any two of the five parameters — Real Power (P), Reactive Power (Q), Apparent Power (S), Power Factor (PF), or Phase Angle (φ). The calculator computes the remaining values in real time as you type. If you fill more than two fields, it uses your two most recently entered values.
Choose units and load type
Use the dropdown beside each power field to switch units — W/kW/MW for real power, VAR/kVAR/MVAR for reactive power, and VA/kVA/MVA for apparent power. Set the Load Type to Lagging (Inductive) for motors and transformers, or Leading (Capacitive) for capacitor banks.
Read the triangle and rating
View the power triangle visualization with the phase angle marked, and check the Power Factor Rating gauge for instant feedback — Poor, Fair, Good, or Excellent. The Formulas Used panel shows the exact equations behind each result.
Size your correction
Set a Target PF (such as 0.95) in the Power Factor Correction panel and the calculator shows the capacitor bank size in kVAR needed to reach it, plus the reactive power before and after. Click any Quick Example to load typical values for a motor, lighting, heater, or AC unit.
Features
Solve from Any Two Values
Enter any two of P, Q, S, PF, or φ and the calculator solves for all remaining power triangle values automatically.
Full SI Unit Support
Switch between W/kW/MW, VAR/kVAR/MVAR, and VA/kVA/MVA per field, with phase angle shown in degrees.
Power Triangle Visualization
An interactive SVG triangle with color-coded sides — P in amber, Q dashed in purple, S in blue — scaled to your values with φ marked.
Power Factor Rating Gauge
A color-coded gauge rates your PF as Poor, Fair, Good, or Excellent so you can judge efficiency at a glance.
Lagging & Leading Loads
Label the calculation for inductive (lagging) loads like motors or capacitive (leading) loads like capacitor banks.
Power Factor Correction
Set a target PF to find the exact capacitor bank size in kVAR needed, with reactive power before and after correction.
Quick Examples
Load typical values in one click for an industrial motor, fluorescent and LED lighting, a heater, an AC unit, or a welding machine.
Adjustable Precision
Choose 2, 3, 4, or 6 decimal places for every result to match the precision your work requires.
Formula Display
Every calculation lists the formulas it used, so you can verify the math or learn how each value is derived.
Real-Time Results
Outputs, the triangle, and the gauge update instantly as you type — no calculate button to press.
Frequently Asked Questions
What is power factor?
Power factor (PF) is the ratio of real power (P) to apparent power (S) in an AC circuit: PF = P / S = cos φ. It measures how efficiently power is used. A PF of 1.0 means all the power does useful work, while a lower value means part of it circulates as reactive power without doing work.
How do you calculate power factor from kW and kVA?
Divide real power by apparent power: PF = kW / kVA. Enter your real power in kW and apparent power in kVA, and the calculator returns the power factor along with reactive power (kVAR) and the phase angle automatically.
What is a good power factor value?
A power factor of 0.85 or higher is generally acceptable, and many utilities require 0.90 or above to avoid penalties. A PF of 0.95 or more is excellent and indicates highly efficient power usage. The rating gauge flags values below 0.70 as Poor.
How do I correct (improve) power factor?
Capacitor banks are installed in parallel with the load to supply reactive power locally, reducing the reactive power drawn from the utility. This raises the power factor, lowers current draw, and cuts costs. Enter your current values, set a Target PF, and the calculator sizes the capacitor bank in kVAR.
How much kVAR do I need to reach 0.95?
The required capacitor size is Q = P × (tan φ₁ − tan φ₂), where φ₁ is your current phase angle and φ₂ is the angle for the target PF. Enter your load values, set the Target PF to 0.95, and the Power Factor Correction panel shows the exact kVAR needed and the reactive power before and after.
What is the difference between lagging and leading power factor?
A lagging power factor occurs in inductive loads such as motors and transformers, where current lags behind voltage. A leading power factor occurs in capacitive loads, where current leads voltage. Most industrial loads are lagging.
Why can't I use PF and phase angle together as inputs?
Power factor and phase angle are directly related (PF = cos φ), so they don't give two independent pieces of information. You need at least one power value (P, Q, or S) combined with either PF or φ to solve the power triangle.
What is the power triangle?
The power triangle is a right triangle where the horizontal side is real power (P), the vertical side is reactive power (Q), and the hypotenuse is apparent power (S). The relationship is S² = P² + Q², the angle between P and S is the phase angle φ, and cos φ equals the power factor.
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