UPS Runtime Calculator
Estimate battery runtime from usable energy, connected watts, efficiency and reserve.
This calculator provides a planning estimate when a detailed manufacturer runtime curve is unavailable.
Because UPS battery performance is nonlinear, confirm the result against the exact model’s official runtime chart.
Enter Battery Watt-Hours and Connected Load
The calculator reduces battery energy for efficiency and reserve, then divides by connected watts.
Calculator Guidance
Use this result for rough planning only. Final selection should rely on the manufacturer’s runtime graph.
UPS Runtime Calculator
Planning estimate only.
How the Estimate Works
The calculator reduces battery watt-hours for efficiency and reserve, then divides by connected watts.
How to Estimate Battery Watt-Hours
Battery watt-hours are approximately voltage multiplied by amp-hours and the number of batteries in the series string where appropriate.
Runtime Examples
| Usable Energy | Load | Estimated Runtime |
|---|---|---|
| 100Wh | 50W | About 1.36 hours |
| 216Wh | 150W | About 59 minutes |
| 432Wh | 300W | About 59 minutes |
| 864Wh | 600W | About 59 minutes |
Why Actual Runtime Differs
High-Load Losses
Battery capacity falls under heavy discharge.
Inverter Efficiency
Changes with load.
Battery Age
Older batteries store less.
Temperature
Affects performance.
UPS Reserve
Shutdown occurs before full depletion.
Runtime Algorithms
Manufacturers use model-specific curves.
How to Use the Result
Add Load Headroom
Do not size at the watt limit.
Check Manufacturer Chart
Confirm exact runtime.
Plan Shutdown Time
Allow software shutdown.
Include Network Gear
May be required.
Account for Aging
Add future margin.
Test the Real System
Perform a controlled outage.
Frequently Asked Questions
Why is runtime nonlinear?
Battery voltage, efficiency and usable capacity change with load.
Where do I find watt-hours?
Check battery voltage, amp-hours and count.
What efficiency should I use?
Around 75–85% is a rough planning range.
How much reserve should I add?
Ten to twenty percent is common.
Why is the official chart better?
It reflects the exact battery and inverter.
Can I size by VA alone?
No, use real watts.