Tech & PC
What size UPS do you need for your PC and router (VA)?
UPS size in VA from the devices you plug in — PC, monitor, router, NAS — with runtime target and standard sizes.
Quick answer
A UPS (uninterruptible power supply) is sized in VA, not watts: add up the devices you want to keep alive during a blackout, add 25% headroom, then divide by the 0.6 power factor typical of consumer units. A gaming PC (~450 W) with a monitor (30 W) and router (15 W) draws about 495 W → 495 × 1.25 ÷ 0.6 ≈ 1,030 VA, so the right shelf size is a 1,200 VA unit — good for roughly 5-10 minutes, plenty of time to save your work and shut down cleanly.
What do you want to keep running on battery?
Recommended UPS
1,200 VA (~720 W)
- Total load
- 495 W
- Estimated runtime at this load
- 5-8 min
Related: not sure how many watts your PC draws? Size the PSU first
Consumer UPS units are rated in VA but deliver roughly 60% of that in watts — the calculation already accounts for it, plus 25% headroom. Never plug a laser printer or space heater into the battery outlets: their heating elements draw surges that overload any consumer UPS. If your PC power supply has active PFC (most quality units today), prefer a pure sine wave model. For 30+ minutes of runtime, a power station is usually smarter than oversizing the UPS.
How it works
The trap is the double rating: an 850 VA line-interactive UPS delivers only about 510 real watts, because consumer units have a 0.6 power factor. Match the watt rating to your load, not the VA on the box. Two more things worth paying for: if your PC has an active-PFC power supply (nearly every quality unit today), choose a pure sine wave model — simulated sine wave can make active-PFC supplies click off at exactly the moment the UPS should be saving you. And remember a UPS buys minutes, not hours: its job is to ride through micro-outages and give you a clean shutdown. If you want the router and NAS up for an hour, a small DC mini-UPS or a power station is the better tool than a monster UPS.
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Frequently asked questions
Why does an 850 VA UPS not deliver 850 watts?+
VA (volt-amperes) is apparent power; watts are real power. The ratio between them is the power factor, and consumer UPS units are built around 0.6: 850 VA × 0.6 = about 510 W usable. Always check the watt rating in the spec sheet and compare that — not the VA — to the total draw of your devices.
How long does a UPS actually last in a blackout?+
Minutes, not hours. A correctly sized unit at 40-60% load typically gives 8-15 minutes — exactly what it’s designed for: bridging micro-outages and letting you save and shut down. Runtime grows fast as load drops (a lone router on a 850 VA unit can run 40+ minutes), but if you need an hour or more, external battery packs or a power station beat any consumer UPS on price.
Can I plug a laser printer into a UPS?+
No — it’s the classic mistake. A laser printer’s fuser heats in pulses that spike well over 800 W, enough to overload the battery outlets of any consumer UPS or trip it mid-print. Same logic for space heaters, kettles and vacuum cleaners. Printers go in the surge-only outlets (most UPS units have both) or a plain surge strip.
Do I need pure sine wave or is simulated fine?+
If your PC power supply has active PFC — true of nearly every 80 Plus unit sold today — pay for pure sine wave. On battery, a simulated (stepped) sine wave can make active-PFC supplies shut down or reboot, defeating the whole point of the UPS. For a router, modem or TV alone, simulated sine wave is fine and cheaper.
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