Published July 2026 · Estimates are calculated from standard replacement-battery nameplate capacities and an 85% inverter efficiency assumption — methodology below. Real runtime varies with battery age and load type (±25% is normal). Always check the manufacturer’s runtime chart before an important purchase.
“What size UPS do I need?” has a two-part answer nobody’s spec sheet gives you straight: the watt rating decides whether the UPS can run your gear at all, and the battery watt-hours decide for how long. VA ratings — the big number on the box — are marketing shorthand for both. This calculator does the actual math.
Rules of thumb: a 600 VA unit runs a 90 W TV + router for roughly 35–45 minutes; a 1500 VA unit runs the same load for roughly 1.5–2 hours. A desktop gaming PC eats any consumer UPS in 10–25 minutes — UPSes buy you a safe shutdown, not a gaming session.
UPS runtime calculator
1. What are you backing up?
2. Which UPS?
How the math works (so you can check it)
Runtime is battery energy divided by load: runtime (hours) = battery Wh × 0.85 ÷ load W. The 0.85 accounts for inverter losses. Battery Wh comes from the standard replacement-battery nameplate for each model (e.g. the APC BE600M1 uses a 12 V 7 Ah battery = 84 Wh). For custom VA inputs we estimate Wh ≈ VA × 0.135 — the ratio that holds across the consumer line-interactive units in the table below. Two honest caveats: batteries fade (a 3-year-old UPS may hold half its rated energy), and loads with power-factor-corrected supplies draw a little differently than nameplate suggests. Treat results as a planning range, not a stopwatch.
Battery capacity by model (the numbers nobody prints on the box)
| UPS | VA / W rating | Replacement battery spec | Energy | 90 W TV+router est. |
|---|---|---|---|---|
| APC BE425M | 425 VA / 225 W | 12 V 4.5 Ah | ~54 Wh | ~30 min |
| APC BE600M1 | 600 VA / 330 W | 12 V 7 Ah | ~84 Wh | ~48 min |
| CyberPower CP800AVR | 800 VA / 450 W | 12 V 9 Ah | ~108 Wh | ~60 min |
| APC BX1500M | 1500 VA / 900 W | 2 × 12 V 9 Ah | ~216 Wh | ~2 h |
| CyberPower CP1500AVRLCD | 1500 VA / 900 W | 2 × 12 V 9 Ah | ~216 Wh | ~2 h |
Shopping from this class? Our best UPS for a TV and home-theater UPS guides cover the picks; the router battery backup guide handles the small end.
UPS sizing FAQ
How long will a 1500 VA UPS run a TV?
A 1500 VA consumer unit carries roughly 216 Wh of battery. For a 90 W TV-plus-router load that works out to about 1.5 to 2 hours new – aging batteries shorten it substantially.
What is the difference between VA and watts on a UPS?
Watts are the real power the UPS can deliver; VA is apparent power and is always the bigger, friendlier number on the box. Consumer units typically support about 60% of their VA in watts – a 1000 VA unit is really a ~600 W unit. Size against the watt rating.
Can a UPS run a refrigerator?
Not usefully. Compressor start-up surges are several times the running wattage and trip or overload consumer UPS units, and the battery would only carry a fridge for minutes anyway. For outage-proofing a fridge you want a generator or a large inverter system, not a UPS.
Do I need pure sine wave output?
For TVs, routers and consoles, a simulated sine unit is generally fine. For desktop PCs with active-PFC power supplies, pure sine is the safe choice – some PFC supplies click over to battery poorly on stepped waveforms.
Why does my UPS run for less time than this calculator says?
Battery age is the usual reason – sealed lead-acid batteries lose capacity every year and a 3-4 year old UPS can be down to half its rated energy. If runtime has visibly collapsed, see our guide to telling when a UPS battery needs replacing.