PF = W / VA

The power factor is the ratio of real power (W) to the apparent power (VA) in the circuit. The higher the number, the more efficient the circuit. In most practical applications the power factor figure is between 0.50 and 0.90.

Real power is the capacity of the circuit to perform work (watts). Apparent power is simply the product of the voltage and current (volt amps) of the circuit. Due to energy stored in the load or due to a non-linear load, the apparent power (volt amps) will be greater than the real power (watts).

Why is this important? A load with a low power factor needs more current to do the same amount of work than a load with a high power factor. This will lead to higher operating  costs and may require higher capital costs for equipment with higher current ratings.

When researching UPS battery backup for a specific application, look at the specifications of the models being considered. Compare units based on the cost of work capacity per dollar (watts / $).