What Size UPS Do I Need for a Router and Modem?

Most people sizing a UPS for their internet gear start from the VA number on the box, because that is the number the box advertises. A 1500VA unit sounds like it should carry a 25W router most of the night. It carries it for about three hours.

The VA rating describes how much load a UPS can supply at once, not how long it can supply it. Runtime comes from the battery, and consumer UPS batteries are small: a 1500VA unit typically holds 135 to 200Wh, roughly the same energy as a mid-range phone power bank scaled up a few times.

Quick Answer

Pick the row that matches how long you need to stay online with a router and modem drawing about 25W:

• Up to 1 hour: a 600VA UPS, the smallest tier worth buying
• 2 to 3 hours: a 1500VA UPS
• 4 to 8 hours: a 300 to 500Wh power station
• 12 hours or more: a 500Wh power station or larger

Above about four hours, spending more on a UPS buys very little extra time. The batteries stop growing long before the price does.

Why VA Does Not Give You Hours

VA (volt-amps) and watts both describe rate: how much a UPS can deliver at any instant. Neither says anything about the size of the tank. A UPS with a 1500VA rating and one with a 600VA rating can hold similar batteries, and two units with the same VA rating can differ by 50% in runtime.

A UPS spec sheet gives three numbers, and only the last one sets runtime:

Number	Typical value	What it tells you
VA rating	600 to 1500VA	The largest load the unit can supply. Marketing leads with this.
Watts	330 to 1000W	The same limit, stated honestly. Always lower than the VA figure.
Battery watt-hours	60 to 200Wh	The energy stored. This sets runtime.

Watt-hours are the number you want, and it is usually the hardest to find on a spec sheet. If it is missing, look for the battery’s volts and amp-hours and multiply them: a 12V 9Ah battery is 108Wh. For why the VA and watt figures differ at all, see Watts vs Volt-Amps.

Real UPS Models, Real Hours

These are units from our UPS comparison table, with runtime at a 25W router-and-modem load. Lead-acid batteries deliver about 40% of their rated capacity in practice, after depth-of-discharge limits and inverter losses.

UPS	Battery	Router only (15W)	Router + modem (25W)	Plus a switch (45W)
APC BE600M1 (600VA)	60Wh	~1.6 hrs	~1 hr	~0.5 hrs
CyberPower CP1000PFCLCD (1000VA)	108Wh	~2.9 hrs	~1.7 hrs	~1 hr
CyberPower CP1500PFCLCD (1500VA)	170Wh	~4.5 hrs	~2.7 hrs	~1.5 hrs
APC SMC1500C Smart-UPS (1500VA)	200Wh	~5.3 hrs	~3.2 hrs	~1.8 hrs
APC SMT3000RM2UC (3000VA)	480Wh	~12.8 hrs	~7.7 hrs	~4.3 hrs

Darker cells mean longer runtime. These are estimates.

Doubling the VA rating does not double the runtime, because the battery does not scale with it. Nothing here clears 7 hours at 25W except a rack-mount model priced for server cupboards, not for the shelf beside a router.

The 12-Hour Question

A common search is some version of “how big a UPS do I need to power a router and modem for 12 hours”. The honest answer is that consumer UPS hardware does not do this. Reaching 12 hours at 25W needs roughly 750Wh of lead-acid battery, which means a rack-mount unit, an external battery cabinet, or several units chained together.

A power station reaches the same runtime for far less, because it spends its cost on storage rather than on instant handoff.

A 500Wh power station runs the same load about four times longer than the 1500VA Smart-UPS above, and usually for less money, though both move with the market: the UPS table carries current prices. The trade is switchover: most power stations pause briefly when wall power drops, which can reboot a router, while a UPS hands over without interruption. See UPS vs Portable Power Station for the full comparison.

Sizing It Yourself

Count everything that has to stay powered, not just the router. A modem and an ONT are separate boxes on separate plugs:

Equipment	Typical draw
Wi-Fi router	8 to 20W
Cable or DSL modem	5 to 15W
Fiber ONT	5 to 12W
Network switch	10 to 30W

Once you have a total, a rough rule covers the UPS case: divide the battery’s watt-hours by your load, then take 40%. A 170Wh UPS at 25W gives 170 ÷ 25 × 0.4, or about 2.7 hours.

Internet gear has no startup surge, so the VA rating is almost never the binding constraint. Any UPS large enough to be worth buying already supplies far more watts than a router needs. Size on the battery, not the badge.

Try It in the Calculator

Setup	4 hours	8 hours	12 hours
Router + modem	Calculate	Calculate	Calculate
Router + modem + switch	Calculate	Calculate	—
Router + fiber ONT	—	Calculate	Calculate

What People Miss

A bigger VA rating mostly buys headroom you already have. Going from 600VA to 1500VA triples the load capacity, which a 25W router will never use. The runtime gain comes from the larger battery that happens to ship alongside it.

Fiber setups need the ONT powered too. A router with an unpowered ONT has nothing to connect to, and the ONT is often mounted away from the router in a garage or utility cupboard.

Mesh nodes are separate devices on separate outlets. Three nodes at 10W each doubles a 25W setup, and only the node next to the UPS stays up.

Lead-acid UPS batteries fade. A three-year-old UPS may deliver half its original runtime, so size with margin if the unit will sit for years between outages.

Your ISP has its own power problem. Street cabinets and cell sites carry limited backup. Powering your gear keeps the local network alive, not necessarily the connection beyond it.

Bottom Line

Size a UPS for a router on battery watt-hours, not the VA rating on the box. At a typical 25W, expect about 1 hour from a 600VA unit and 3 hours from a 1500VA unit.

If the target is longer than about four hours, stop shopping for a UPS. A 300 to 500Wh power station runs several times longer for a similar outlay, at the cost of a brief switchover gap. Compare both on the UPS table and the main product list, where prices refresh twice daily. For the model-by-model method, read How Long Will a UPS Run?; for the wider desk setup, see What Size UPS Do I Need for a Home Office?.