UPS Runtime Calculator
Estimate ideal battery-backup time from stored energy and connected load. Compare this approximation with your UPS manufacturer’s runtime curve.
Estimated runtime
Battery age, discharge rate, inverter cutoff and UPS design affect runtime. Use manufacturer runtime curves for critical equipment.
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How this calculator works
Watt-hours describe the stored energy available before conversion losses. If a battery rating is in amp-hours, multiply it by nominal voltage first. Dividing usable energy by load gives an idealized runtime. High discharge rates, battery wear and low-voltage cutoff can cause actual runtime to be substantially shorter.
Formula
runtime hours = battery Wh × efficiency / load W
Assumptions & limitations
Battery age, discharge rate, inverter cutoff and UPS design affect runtime. Use manufacturer runtime curves for critical equipment.
Worked example
100 Wh at 80% efficiency and 200 W gives 24 minutes.
Our approach to calculations ↗Common questions
Can I use the UPS VA rating as battery capacity?
No. VA is an apparent-power rating, not stored energy. Enter battery watt-hours or amp-hours and nominal voltage.
Why can real runtime be shorter?
Battery age, discharge rate, inverter losses and cutoff can reduce usable energy. Manufacturer runtime curves are more suitable for critical systems.
How are amp-hours converted?
Multiply amp-hours by nominal battery voltage to estimate watt-hours, then apply the entered efficiency.