Fator de Potência
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
cos φ = P/S
About this calculator
The power factor calculator determines the cosine of the phase angle between voltage and current in AC circuits. The power factor is the ratio of active power (P), measured in watts, to apparent power (S), measured in volt-amperes. A power factor near 1 indicates efficient energy use, while low values indicate reactive losses.
To calculate, enter values for active power (in W) and apparent power (in VA). The formula is cos φ = P / S. The result is a number between 0 and 1. For example, if P = 800 W and S = 1000 VA, the power factor is 0.8. This measurement is essential in industrial and commercial electrical installations.
When to use: when sizing capacitor banks for power factor correction, analyzing energy bills (penalties for low power factor), or checking the efficiency of motors and transformers. Cautions: ensure units are correct (W and VA). The calculation assumes ideal sinusoidal conditions; non-linear loads may introduce harmonics that distort the measurement.
Frequently asked questions
What does a power factor of 1 mean?
It means voltage and current are in phase, so all supplied power is converted into useful work. It is the ideal for electrical systems.
How to correct a low power factor?
Usually capacitor banks are used to compensate for inductive reactive power. Consult an electrical engineer for proper sizing.
What is the difference between active, reactive and apparent power?
Active power (P) does work; reactive power (Q) maintains magnetic fields; apparent power (S) is the vector sum of both.
Can the power factor be negative?
Yes, if the load is capacitive, the phase angle is negative, resulting in a negative power factor. The absolute value is usually considered for efficiency.
Why do utilities charge penalties for low power factor?
Because low power factor increases network losses and requires greater generation and transmission capacity, burdening the system.