Understanding Power Factor
Power factor measures how efficiently electrical power is converted to useful work. Low PF means more current is needed for the same power output, increasing losses and costs.
Power Factor Calculator
Our power factor calculator helps electrical engineers and facility managers understand and optimize AC power systems. Calculate the relationship between real, reactive, and apparent power, determine capacitor requirements for PF correction, and reduce electricity costs from power factor penalties.
star
4.7
calendar_today
Updated: October 2025
auto_awesome
AI Insights
AI
New
Power Factor Calculator calculator
kW
kVA
V
Results
0.75
Power Factor (75%)
Real Power
100 kW
Reactive Power
88.19 kVAR
Apparent Power
133.33 kVA
Phase Angle
41.41°
Line Current
160.4 A
Capacitor Needed
55.26 kVAR
Current Reduction
21.05%
electric_meter Power Factor Rating
Excellent
0.95 - 1.0
Good
0.85 - 0.95
Average
0.70 - 0.85
Poor
< 0.70
bolt Typical PF Values
Resistive Load
1.0
Induction Motor
0.7-0.85
Fluorescent Lights
0.5-0.6
How to Use the Power Factor Calculator
1
Select Mode
Choose to calculate PF, power values, or correction requirements
2
Enter Power Data
Input real power (kW) and apparent power (kVA) or existing PF
3
Set Target PF
For correction mode, enter desired power factor
4
View Results
See all power values and capacitor sizing if applicable
The Formula
Power factor indicates how effectively electrical power is used. PF = 1 (unity) means all power does useful work. Low PF means reactive power is wasted. S² = P² + Q² (power triangle).
Power Factor (PF) = Real Power (kW) ÷ Apparent Power (kVA)
lightbulb Variables Explained
- PF Power Factor (0 to 1, or 0% to 100%)
- P Real Power in kW (actual work done)
- Q Reactive Power in kVAR (energy stored/returned)
- S Apparent Power in kVA (total power flow)
- θ Phase angle between voltage and current
tips_and_updates Pro Tips
1
Unity (1.0) power factor means 100% efficient power use
2
Industrial facilities aim for PF > 0.95 to avoid utility penalties
3
Motors and transformers cause lagging (inductive) power factor
4
Capacitors correct lagging PF; inductors correct leading PF
5
Oversized motors running at light load have poor PF
6
LED and VFD loads may have leading PF
7
Power factor correction reduces electricity bills and line losses
Power factor is a measure of how effectively an AC electrical system converts current into useful work, expressed as a ratio between 0 and 1 (or 0% to 100%). A power factor of 1.0 means all the current drawn from the supply is being used productively; a power factor of 0.7 means only 70% of the apparent power is doing real work, while the remaining 30% circulates as reactive power — wasted capacity that heats conductors, overloads transformers, and increases utility bills without performing useful work. In AC circuits, real power (measured in kilowatts, kW) does actual work like running motors and heating elements, while reactive power (measured in kVAR) sustains magnetic fields in inductive loads like motors, transformers, and fluorescent ballasts. Apparent power (kVA) is the vector sum of both. Most industrial facilities operate at power factors between 0.75 and 0.90, and utilities penalize customers who fall below 0.85-0.90 with surcharges that can add 10-25% to electricity bills. Power factor correction — typically achieved by adding capacitor banks that supply reactive power locally — reduces these penalties, frees up transformer capacity, and lowers I²R losses in cables. Calculating the required capacitor size in kVAR to raise power factor from a current value to a target value is one of the most common electrical engineering calculations.
Power Factor Correction Benefits
Improving PF reduces utility bills, decreases line losses, increases system capacity, and avoids penalty charges. Typical target is 0.95 or higher.
Frequently Asked Questions
Related Tools
View all Engineering View all arrow_forward
sell
Tags
verified
Data sourced from trusted institutions
All formulas verified against official standards.