UPS Runtime Calculator
Estimate UPS backup runtime in minutes from battery watt-hours (or VAh × power factor), load, and inverter efficiency.
Processed locally in your browser — nothing is uploaded.
Sum of battery voltage × Ah for all internal batteries.
~85% is typical for line-interactive UPSes.
Used only to warn about overload.
Results
- Estimated runtime
- 85 min
- Usable energy at the outlet
- 425 Wh
Real UPS runtimes are nonlinear — batteries deliver less energy at high discharge rates, so heavily loaded units run noticeably shorter than this linear estimate, and lightly loaded ones often run longer. Check the manufacturer's runtime chart for critical loads.
About UPS Runtime Calculator
Enter the battery energy in Wh (or VAh with the power factor from the spec sheet), your load in watts, and the inverter efficiency (~85% is typical). The estimated runtime is battery energy × efficiency ÷ load. An optional UPS wattage field warns when the load exceeds what the unit can deliver at all.
Common uses
- Check whether a UPS keeps a router and NAS alive long enough to shut down cleanly
- Compare runtime between a 600 VA and 1500 VA unit for the same PC
- Decide how much load to shed to reach a runtime target
Example
Input
500 Wh battery · 300 W load · 85% efficiency
Output
≈ 85 minutes
Limitations
- Real UPS runtimes are nonlinear — heavy loads drain batteries disproportionately fast, so manufacturer runtime charts beat this linear estimate near full load.