Most people size their UPS battery by budget or by whatever the shop has on the shelf that day. The better approach takes ten minutes with a pen and paper — add up what you actually want to run, decide how many hours you want it to last, and the right battery size becomes obvious. Here's exactly how to do that.
WHAT'S IN THIS GUIDE
The Backup Calculation Formula
Three numbers decide the battery size you need: your total load in watts, how many hours of backup you want, and your system's voltage.
Round up to the nearest available battery size, and add a small buffer for inverter inefficiency.
Typical Appliance Power Draw
Use these as a starting point — check the actual rating on your own appliances where possible, since wattage varies by model.
| Appliance | Typical Wattage |
|---|---|
| LED Bulb / Tube Light | 10–20W each |
| Ceiling Fan | 60–80W each |
| Wi-Fi Router | 10–15W |
| LED TV (40") | 60–100W |
| Refrigerator | 150–250W (higher on startup) |
| Laptop Charger | 45–65W |
| Split AC (1 Ton, inverter) | 900–1200W |
A Worked Example for a Lahore Home
Say a typical household wants to run 4 LED bulbs, 3 fans, a router, and a TV during an outage, for 6 hours, on a 12V system:
(362W × 6 hrs) ÷ 12V ≈ 181Ah — rounding up, a 200Ah battery (or two 100Ah batteries in parallel) covers this load with a small safety buffer.
Recommended Battery Sizes by Home Type
Lights, fans, router, and a TV for 4–6 hours — typical for a 2-3 room apartment.
A full house's lights and fans plus a fridge and a couple of TVs for 5–7 hours.
Whole-home coverage including a fridge, multiple TVs, and longer backup windows.
Tips for a More Accurate Estimate
- Check the actual label on your appliances where possible — wattage varies more than people expect between models.
- Don't include appliances you won't actually run on backup — sizing for everything in the house inflates the battery size unnecessarily.
- Add roughly 15-20% buffer to your calculated Ah for inverter inefficiency and battery aging over time.
- Consider your area's typical outage length, not just a worst-case scenario — sizing for 8 hours when outages rarely exceed 3 adds unnecessary cost.
- Match the battery type to how you'll use it — frequent, longer outages favor tubular or lithium over basic flat-plate batteries. Our UPS battery guide breaks down the types.
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Frequently Asked Questions
How do I calculate the UPS battery size I need for my home?
Add up the wattage of everything you want to run during an outage, multiply by the hours of backup you want, then divide by your system voltage to get the amp-hour (Ah) rating you need.
What size UPS battery is best for a small home in Lahore?
For lights, fans, and a router with 4-6 hours of backup, a 100Ah to 130Ah battery is typically sufficient for a small home. Larger homes with more appliances need higher Ah ratings.
Does a bigger UPS battery always mean longer backup?
Generally yes, but backup time also depends on your actual load — a higher Ah battery running a heavy load will still drain faster than the same battery running a lighter one.
Ready to size your home backup?
Call or WhatsApp us at +92 321 6509001 — we're at 367-F1 Samsani Road, Johar Town, Lahore.