UPS Battery Calculator
Calculate the battery capacity needed for your UPS to provide the backup you want.
About the UPS Battery Calculator
Whether you are comparing options or just need a quick check, the UPS Battery Calculator delivers an accurate result instantly, with every input editable so you can model your own scenario.
A UPS keeps the essentials running through load-shedding — but only if it is sized correctly for your load and backup needs. This UPS Battery Calculator sizes a UPS system from the appliances you need to power and the backup hours you want.
The calculation combines the load wattage and the desired backup time to arrive at the battery capacity and UPS rating required, using the standard relationship between watts, battery volts and amp-hours.
The most common UPS mistake in Pakistan is buying on the VA rating without checking the battery: two 'same size' UPS units can differ hugely in backup time because battery capacity varies. This tool sizes the battery, which is what actually determines runtime.
Remember the 50% rule for lead-acid batteries: plan for discharge down to about half capacity to protect battery life. The calculator's result reflects usable capacity, so the backup time it shows is realistic.
The UPS Battery Calculator is one of a large, connected suite of Pakistani calculators on GuruAlpha, so if a related figure comes up next, the tool for it is a click away.
How to size a UPS
- 1
Enter the load — the total wattage of fans, lights and other essentials.
- 2
Enter the backup hours you want during an outage.
- 3
Read the UPS rating and battery capacity required, updated live.
Frequently Asked Questions
How do I choose a UPS battery?
Battery Ah = load × backup hours ÷ voltage, plus ~30% margin. A 600 W load for 4 hours at 12 V needs about 260 Ah.
How many watts does a typical UPS load need?
Two fans (~150 W total), three LED bulbs (~25 W) and a TV (~100 W) add up to roughly 275 W. A 1–1.5 kVA UPS covers this with room to spare.
Why does my UPS backup time drop after a year?
Lead-acid batteries lose capacity with age and deep discharges. Keeping discharge above 50% and avoiding heat extends battery life significantly.