MB Networks
UPS · Runtime · Battery
How long will your UPS last?
Select your UPS model and connected equipment — estimated runtime and load percentage update instantly.
Est. runtime
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Load
0W
Battery
0Wh
UPS
UPS model — or enter values manually below
Connected load
Device preset — or enter wattage manually below
Why VA rating isn't the number that matters
UPS units are marketed by VA (volt-amperes) rating, but actual runtime depends on watts, and the two aren't the same — VA is typically about 1.6× higher than the equivalent watts due to power factor. A "1500VA" UPS is often closer to 900W of real usable capacity, not 1500W. Runtime calculations that use VA directly instead of converting to real watts overestimate how long the UPS will actually last under load.
Why runtime drops faster than load rises
UPS battery runtime isn't linear with load — inverter efficiency drops as load approaches the unit's rated maximum, so pushing a UPS toward its rated capacity costs disproportionately more runtime than the load percentage alone suggests. Sizing a UPS with real headroom (running it at 40–60% of rated capacity rather than close to 100%) gets meaningfully more runtime per watt-hour than running it near its limit.
What's the difference between VA and watts on a UPS spec sheet?
VA (volt-amperes) is the UPS's marketed rating; watts is the actual real power capacity, and VA is typically about 1.6× higher due to power factor. A “1500VA” UPS often provides closer to 900W of real usable capacity — always size and calculate based on watts, not the VA number.
Why does my UPS runtime drop so much faster near full load?
Inverter efficiency isn't constant across the load range — it declines as load approaches the unit's rated maximum, so runtime per watt-hour gets worse, not just proportionally lower, as you push a UPS toward its limit. Sizing with real headroom (running well under rated capacity) gets meaningfully better runtime per watt-hour.
How do I find the actual wattage of my connected equipment?
Check each device's power supply label for rated watts (not amps alone — multiply amps by voltage if only amps is listed), or better, measure real draw with a plug-in power meter, since actual sustained draw is usually well below the label's peak rating.
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Open →Runtime estimates assume ~90% inverter efficiency and a fully charged battery at 20°C. Actual runtime varies with battery age, temperature, and load type.