Convert real power to apparent power
500W computer load
÷ 0.65 PF = 769VA
+ 25% margin = 962VA
→ Choose 1000VA UPS
When sizing UPS systems or generators, you need to convert from watts (what your equipment consumes) to VA (how the device is rated). VA is always equal to or greater than watts.
VA = Watts / Power Factor. Lower power factor means you need more VA capacity for the same watt load.
Divide watts by power factor: VA = W / PF. Example: 800W at PF 0.8 requires 800 / 0.8 = 1000VA capacity.
At PF 1.0 (resistive): 500VA. At PF 0.8: 625VA. At PF 0.6 (computers): 833VA. Always add 20-30% safety margin.
VA includes reactive power from inductive or capacitive loads. The current and voltage get out of phase, so more current flows than needed for the real power consumed.
1) Add watts of all equipment. 2) Divide by power factor (0.6-0.7 for computers). 3) Add 25-30% safety margin. 4) Choose next larger standard UPS size.