How to Calculate Power Factor
What is Power Factor?
Measures reactive vs. real power in AC circuits showing energy efficiency. Power factor <1 wastes electricity and increases utility costs.
Formula
Power factor = P ÷ S
- P
- P value — Variable used in the calculation
- S
- S value — Variable used in the calculation
Step-by-Step Guide
- 1Real power (P) in watts
- 2Apparent power (S) in VA (volts × amps)
- 3Power factor = P ÷ S
- 4Cosine of phase angle between voltage and current
- 5Range 0-1; closer to 1 is better
Worked Examples
Input
P=1000W, S=1200VA
Result
PF=0.833
Common Mistakes to Avoid
- ✕Assuming residential power factor matters (most don't measure)
- ✕Not measuring true power with calibrated meters
Frequently Asked Questions
How does low power factor increase costs?
Utilities charge penalty for PF <0.95; also increases I²R losses in distribution.
How do I improve power factor?
Add capacitors to offset inductive loads (motors, transformers) or use synchronous motors.
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