UPS Calculator
Right-size a UPS for your PC. Enter system wattage and the runtime you want to get a recommended VA rating and a realistic battery runtime.
Sizing a UPS for a PC
Uninterruptible power supplies are rated in volt-amps (VA), not watts. The two are related by the power factor of the load — typically around 0.6 for a conservative estimate on a consumer UPS, so a 450 W system needs roughly 750 VA of capacity before you account for runtime at all.
A UPS is for shutting down, not carrying on
The realistic goal is five to fifteen minutes: enough to save your work, quit cleanly and power down, or to ride out a brief flicker. Sizing for an hour of gaming means a battery bank several times the price of the PC. Runtime also falls sharply as load rises — a unit rated for 30 minutes at half load may give only 8 minutes at full load.
Line-interactive versus pure sine wave
Cheaper units output a stepped or "simulated" sine wave on battery. Most modern power supplies use active power factor correction, and many APFC units dislike a stepped waveform — they can shut down or make an audible buzz on transfer, which defeats the purpose entirely. For a desktop with a modern PSU, a pure sine wave UPS is the safe choice.
What to plug in, and what not to
Put the PC and one monitor on the battery-backed outlets. Leave printers, speakers and phone chargers on the surge-only sockets — a laser printer in particular can draw more on warm-up than the whole UPS is rated for. Do not daisy-chain a power strip into a UPS.
Batteries wear out
The sealed lead-acid batteries in most consumer units last three to five years, and their capacity fades steadily through that life. A unit that once gave 15 minutes may give four by year four. Test yours occasionally rather than discovering the problem during an outage.
Frequently asked questions
What size UPS do I need for a gaming PC?
For a typical 450W system plus a monitor, a 1000-1500 VA pure sine wave unit gives around 8-15 minutes - comfortably enough to save and shut down. Sizing for longer gets expensive quickly.
What is the difference between VA and watts?
Watts is real power consumed; VA is apparent power the unit must supply. For consumer UPS units the ratio is typically 0.6, so a 1000 VA model handles roughly 600W. Always check both numbers on the box, because manufacturers advertise the larger one.
Do I need a pure sine wave UPS?
For a modern desktop, yes. Power supplies with active PFC often refuse to run on a stepped-wave output, shutting down or buzzing on transfer. The premium is modest and it is the difference between a UPS that works and one that does not.
Can a UPS run my PC during a long outage?
Not realistically. Consumer units are designed for minutes, not hours. If you need to keep working through extended outages, a generator or a large battery station is the right tool.