To find what size UPS you need for a home office, add up the watts of everything you’ll plug into it, then pick a unit rated for about 30 to 50 percent more than that total. For a typical desktop, monitor and router, that usually lands somewhere in the 600 to 1,000 VA range.
That’s the short version. Let’s walk through the math so you can do it for your own desk.
Watts versus VA: what’s the difference?
You’ll see two numbers on every UPS: VA (volt-amperes) and watts. Watts tell you how much real power the unit can deliver. VA is a bigger, “apparent” number. For home electronics, the watt rating is the one that matters most, and it’s usually about 60 to 70 percent of the VA figure.
So a unit rated 1,000 VA might handle only 600 watts or so. Always check the watt rating before you buy.
How to add up your power needs
Look at the label or power adapter on each device. You’ll often see a wattage, or volts and amps you can multiply together. Here are some rough, typical ranges:
- Desktop PC: about 100 to 400 watts, depending on the graphics card.
- Laptop: roughly 30 to 90 watts while charging.
- Monitor: around 20 to 60 watts each.
- Router and modem: about 10 to 25 watts together.
- Desk lamp or phone charger: a few watts, though it’s best to leave them off the UPS.
Add the numbers, then multiply by 1.3 to 1.5. That extra room covers power spikes and keeps the UPS from running at its limit, which is gentler on the battery.
What should go on the battery side?
Here’s a tip that saves money: only plug in what has to stay on. Your computer, monitor, modem and router belong on battery outlets. A printer is a bad idea, especially a laser model, because it can pull a big burst of power when it warms up.
Most units have two kinds of outlets: battery backup and surge-only. Use the surge-only ones for the printer and other gear that can wait out an outage.
How long will the battery last?
Runtime depends on your load. A UPS at half its rated watts usually runs for a handful of minutes, and at a light load, such as a laptop and router, it can last much longer. Manufacturers publish a runtime chart for each model, so check yours against your real wattage.
Now, don’t expect to work through a long blackout. A UPS gives you time to save your files and shut things down safely. If you want more runtime than that, you’ll need a larger unit or an extra battery pack.
A quick example
Say you have a desktop that draws about 200 watts, one monitor at 30, and a modem plus router at 20. That’s 250 watts. Multiply by 1.4 and you get 350 watts, so a unit with a watt rating of 400 or more fits, which typically means a 650 to 850 VA model.
Other things that affect the size you need
Watts are the starting point, but a few other details can nudge your choice up or down.
- Plans to grow: if you might add a second monitor or a faster PC next year, buy a bit of extra capacity now.
- Power quality: if your lights flicker often, a model that corrects small voltage changes is worth a look.
- Display and alerts: a screen that shows the load and remaining runtime takes the guesswork out of it.
- Outlets: count how many battery-backed outlets you need, and leave one spare.
- Noise: some units hum or beep. If your desk is in a bedroom, check that the alarm can be muted.
Don’t forget to test it
A UPS you’ve never tested is a UPS you can’t trust. After you set it up, try a quick test: with your work saved, unplug the UPS from the wall and see that everything stays on. Plug it back in right away, and don’t test it with a laser printer or heater attached. Do this once every few months, and your battery’s condition won’t be a surprise.
Most units also have a software option that shuts your computer down on its own when the battery runs low. If you ever step away from your desk during an outage, that feature can save your files while you’re out of the room.
Put it where it can breathe
UPS units make heat while charging, so don’t tuck one into a closed cabinet or bury it under papers. Keep it on the floor or a shelf with open space around it, away from heaters and direct sun. A cooler battery lasts longer, and that means fewer replacements.
Frequently asked questions
Is a bigger UPS always better?
Not necessarily. A larger unit gives you more runtime and headroom, but it costs more and takes up more space. Match it to your load with some extra room.
Can I plug a power strip into a UPS?
It’s best not to. Daisy-chaining can overload the unit and may void the warranty, so plug devices directly into the UPS outlets.
How often should I replace a UPS battery?
Most batteries last around three to five years. If the unit beeps a battery warning or runs only for seconds, it’s time for a new battery.
The bottom line
Add up your watts, add a buffer and choose a UPS that covers your must-keep-running gear. When you’re ready to shop, see our list of the best UPS battery backup for home office setups. On a tighter budget? Try the best budget UPS battery backups for home offices. Planning for the whole house? Our best UPS battery backups for home backup guide covers that. And to see how a UPS differs from a surge protector, read our UPS vs surge protector explainer.