Runtime baseline

Translate a critical load and outage window into battery Wh

Watts multiplied by time produces delivered energy. Nominal battery capacity must be larger because not every stored Wh reaches the connected load.

Separate delivered energy from nominal battery capacity

The energy used by the load is watts × hours. The planner adds the shutdown reserve, then divides by the entered conversion efficiency and usable battery share. The resulting nominal Wh is a comparison floor, not a promise about one UPS model.

Keep a realistic margin

Battery condition, temperature, output conversion, and load behavior change real runtime. Use a measured outage test to replace planning assumptions once an equipment path exists.

Frequently asked questions

How do I convert watts and outage hours into battery size?

Multiply watts by hours, add the shutdown reserve, then divide by conversion efficiency and usable battery share. The result is a nominal Wh comparison floor, not a promise about one UPS model.

Why is nominal battery Wh larger than the energy my load uses?

Not every stored Wh reaches the connected load. Conversion losses and the usable share of the battery mean the nominal capacity must be larger than the delivered energy.

Can I trust the runtime printed on the UPS box?

Treat it as a starting claim, not a measurement. Battery condition, temperature, output conversion, and load behavior change real runtime; verify with a measured outage test.

Continue planning

Turn the power concern into a visible continuity boundary.

Use the planner to keep critical load, runtime, battery reserve, and safe shutdown in one checkable baseline.

Calculate a battery baseline

Critical load

Choose critical loads before sizing a home UPS

Shutdown proof

Reserve UPS time for safe NAS and home-server shutdown

Editorial record

Maintained by Make Your Own Tools to turn “Keep critical home tech running” into a defined continuous watts, battery wh, shutdown reserve, and the next proof check. The references below provide the technical context for this planning path. Its calculation rules and planning assumptions are documented in the methodology, and affected calculations pass regression checks before the review date advances.

Last reviewed
Evidence set
1 primary reference
Calculation coverage
1 affected rule checked
Read methodology →View change history ↗
Planning scope
Home UPS and battery continuity energy planning before an exact product comparison.
Next check
Confirm actual runtime with the installed battery condition, load mix, output mode, and manufacturer procedure.
U.S. Department of Energy: Uninterruptible Power SuppliesDefines a UPS as a battery-backed power system that maintains load continuity when input power fails.Open source ↗