Guide · 2026-11-11
How to size a UPS for a gaming PC
Start with the watts the PC actually draws, not the number on the power supply. An 850 W label is what that supply is allowed to deliver. A game that pulls 400 W from the wall does not become an 850 W UPS problem. If you do not have a wall meter, the PSU calculator is a plan of that draw. Headroom explains why that plan is not the same thing as the supply's label.
Hours come from watt-hours
Usable watt-hours are the battery watt-hours times inverter efficiency. Runtime is that number divided by the load. A 90 Wh battery at 85% efficiency has 76.5 Wh to give. At 400 W that is a short ride, which is why a PC UPS is often a save-your-work device rather than an evening of play. The 85% figure on the UPS calculator is a planning assumption for many line-interactive units. It is not a measurement of the unit in the box. If the maker prints a different efficiency, type that.
VA is not watts
A VA rating is not a watt rating. A PC supply with active power-factor correction still needs VA at least equal to watts divided by the power factor. The calculator's opening power factor is 0.95, labeled as an assumption for that kind of supply, and you can change it. The suggested watt size is the next standard size at or above 1.25 times the load, so the UPS is not specified exactly at its ceiling. That 25% is a planning rule in the tool, not a catalog of models. WattWise does not recommend a UPS by name.
A power station is the other calculator
A Jackery, EcoFlow, BLUETTI, or Anker is not this page. Those stations are sized in RunTime from a published watt-hour rating. How to read a power station label is the companion. The UPS tool stays with battery watt-hours, inverter efficiency, and the VA the PC asks for.