Planning tool
UPS and battery sizing
Enter what is plugged into the UPS and how long it must keep running. The calculator adds growth, converts watts to kVA, and sizes the battery bank.
Result
UPS size
3kVA
Needs 2.67 kVA (2,400 W ÷ 0.9 power factor)
UPS output at that size
2.7kW
Load on the UPS
89%
Batteries
24× 12 V 9 Ah
8 in series × 3 strings, 96 V bank
Battery energy installed
2.59kWh
Needed 2.08 kWh after depth of discharge and ageing
- Check:The load would use more than 80% of the UPS. Choose the next size up or reduce the load.
Method
How the numbers are worked out
From watts to kVA
A UPS is rated in kVA, and the usable power is kVA times its power factor. The calculator divides your design load (with growth) by that power factor, then picks the next standard UPS size.
Battery energy
Energy from the battery equals load × runtime ÷ inverter efficiency. That is divided by the usable share of the battery (80% for sealed lead-acid, so it is not drained flat) and multiplied by an ageing margin (1.25 for lead-acid, the common design factor, so it still delivers late in life).
Counting batteries
Amp-hours needed at the bank voltage set how many parallel strings of 12 V batteries are required; each string has bank voltage ÷ 12 batteries in series.
Assumptions and limits
- Runtime is for a fully charged, new battery at about 25 °C. Heat shortens battery life.
- Battery runtime is not perfectly linear with load; the battery maker's discharge tables decide the final count.
- Sizes shown are generic standard ratings. The UPS and battery data sheets confirm what fits.
- Recharge usually takes 6 to 10 hours; ask for the charger rating if outages come close together.
Related
Nothing you type here leaves your device unless you choose to send it to us. These are planning estimates; a survey or the equipment data sheet confirms the final figures.
Want an engineer to check it?
Send us what you worked out and we will come back with a design based on the real site.