UPS & IPS load calculator
Set how many of each device you want to keep running and for how long. We work out the UPS size and the battery to look for.
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How the load calculator works
UPS size (VA) = total watts ÷ 0.7 power factor × 1.25 headroom, rounded up to the next standard size. Battery (Ah) = total watts × hours ÷ 0.85 inverter efficiency ÷ battery voltage ÷ 0.7 usable capacity.
Load calculator questions
How do I calculate the UPS size I need?
Add up the running watts of every device, divide by the UPS power factor (about 0.7) and add about 25 % headroom. The result is the VA rating to look for; pick the next standard size up.
How do I work out the battery for my backup time?
Multiply the total watts by the hours of backup and divide by the inverter efficiency (about 85 %). Divide that by the battery voltage and by 70 % usable capacity to get the ampere-hours (Ah).
UPS or IPS: which do I need?
A UPS with built-in batteries covers short power cuts of 5–30 minutes for computers. For an hour or more, or for fans and lights during load-shedding, choose an IPS or online UPS with external batteries.