kW vs kVA and power factor explained: the math buyers get wrong, why kW capacity is what counts, and how to read a UPS rating correctly.
Technology Explainers
The single most common UPS sizing mistake in India is confusing kVA with kW. Buyers see "10 kVA" and assume 10 kW of usable power — then wonder why the UPS struggles. The gap between the two is power factor, and understanding it is the difference between a UPS that fits and one that overloads.
kVA vs kW: The Core Difference
kVA (apparent power) is the total power the UPS handles. kW (real power) is the actual work delivered to your load. They are linked by power factor (PF):
kW = kVA × power factor
A UPS rated at a 0.8 power factor delivers 0.8 kW for every 1 kVA. So a 10 kVA / 0.8 PF UPS provides 8 kW of real power — not 10 kW. Paradyne's online UPS is rated at a power factor of 0.8 lagging to unity, which is exactly how you should read its real capacity.
Two Power Factors, Don't Confuse Them
UPS rated (output) power factor — how much real power the UPS can deliver per kVA. This sets your usable kW.
Load power factor — a property of your equipment. Modern IT power supplies run near 0.9-0.99; motors and older gear can be 0.6-0.8.
You must match these. If your load needs 8 kW, a 10 kVA UPS at 0.8 PF covers it; a UPS with a lower rated PF would not.
How to Size Correctly
Add up your real load in watts (kW), not VA.
Convert to the UPS rating: kVA needed = kW ÷ UPS rated power factor.
Add 20-30% headroom for startup, growth, and to avoid running at 100%.
The full worked method is in how to calculate UPS capacity.
Why Vendors Quote kVA
kVA is the bigger, better-looking number, so it dominates marketing. Insist on the kW rating and the rated power factor together — that is what determines whether the UPS carries your load. Distorted current (high THD) also drags down effective power factor; see UPS harmonics and THD.
The Takeaway
Always size in kW, then convert to kVA using the UPS rated power factor.
Read "10 kVA at 0.8 PF" as 8 kW of usable power.
Match UPS rated PF to your load and add headroom.
Unsure of your real kW load? Our team will work it out and recommend the right rating.
