UPS sizing tool
What size UPS do you need?
Enter your load and backup time for an indicative kVA rating. Every step of the calculation is shown, so you can see exactly how the figure is reached.
How it works
About the calculation
Why divide by power factor?
UPS ratings are given in kVA (apparent power), while equipment is usually rated in watts (real power). Dividing watts by the power factor converts one to the other. Many UPS and IT loads are around 0.8–0.9; if you are unsure, 0.8 is a cautious choice.
Why add headroom?
Running a UPS close to 100% leaves no margin for start-up surges, measurement errors or equipment you add later. A margin of 20–25% is a common rule of thumb.
Does this calculate the battery bank?
Yes, as an estimate: it shows how many 12 V batteries and what Ah rating you would need, using a typical DC voltage for that UPS size. It allows for faster discharge on short backup times and adds 25% for battery ageing. The exact bank depends on the UPS model and battery brand, so our team confirms it when quoting.
Motors, pumps and compressors?
Inductive loads can draw several times their rated power when starting. If your load includes motors, mention it when you send the result so our team can size for start-up current.