What size UPS do I need for a computer and router?
Size it from the summed wattage of the devices you want to keep alive, plus headroom.
A home setup is usually a desktop or laptop plus a router, sometimes a modem and a small switch. Add the wattage printed on each device's label, then add roughly 25–30% headroom so the unit is not running at its limit.
A laptop and router together often draw well under 100 W, while a desktop with a monitor can sit in the 200–400 W range. The UPS rating you buy should exceed the total, but the runtime you get depends on how close the load sits to that rating.
Runtime scales inversely with load: a unit loaded at half its rating runs substantially longer than one loaded near its ceiling. Buying twice the capacity you need buys minutes, not hours.
- List every device you want protected, including the router and modem.
- Read the wattage or amperage from each label and convert to watts (volts × amps).
- Sum the values and add 25–30% headroom.
- Choose a UPS rating at or above the total.
- Check the runtime curve at your actual load, not at the unit's full rating.
Why is runtime measured in minutes?
A UPS bridges a gap; it is not meant to power a setup for hours.
On-battery runtime for most units is short — typically 5 to 15 minutes — because the job is defined by what has to happen before power returns or a backup source starts.
Within those minutes you can save documents, let the operating system finish writing to disk, and shut down cleanly. Starting a standby generator or transferring to another supply also fits inside this window.
Runtime quoted for a UPS always refers to a specific load. The same unit measured at 50% load will report more minutes than at full load.