## UPS » Power Factor

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### The power rating of a UPS in watts is a function of its
power factor.

**Power Factor** - Power Factor is expressed as
the difference between “apparent power” and “real power”. A 1,000 VA UPS
with a 0.9 power factor will be rated for a 900 watt load. A 1,000 VA UPS
with 0.7 power factor will be rated for a 700 watt load. The amount of
work that a UPS can perform is expressed in watts. Therefore, a UPS with a
higher power factor is capable of more work than a UPS with a lower one - given
the same amount of voltage and amperage (VA). This can be visualized as a
glass of beer with foam on the top. The full glass of beer + foam
represents the volt-amps (VA), or apparent power. The beer itself represents the watts, the
portion of the contents that can do work.

**Efficiency** - Efficiency is the difference
between watts in and watts out. For instance, a UPS that requires a 100 watt input
to do 96 watts of work output would be 96% efficient. The 4% inefficiency
is energy lost primarily in the form of heat.

When trying to figure out which UPS is the right size for
a particular application look at the wattage specification. The UPS
with the lowest price per watt is the best value.