How to Size Your Home Backup, Room by Room (with a Worksheet)
Total your real load room by room, then convert it to the exact inverter and battery size.
The cleanest way to size a backup system is to stop guessing and add up what you actually use. Here's the same room-by-room method we use at the counter — do it in five minutes and you'll know your exact inverter and battery.
Step 1: Walk through each room
For each room, write down only what you genuinely need during a cut — usually fans, a few lights, and shared items like the TV, Wi-Fi and fridge.
Step 2: Use these typical wattages
| Appliance | Typical watts |
|---|---|
| Ceiling fan | 75 W |
| Tube light | 40 W |
| LED bulb | 10 W |
| LED TV | 100 W |
| Wi-Fi router + set-top box | 35 W |
| Refrigerator | 200 W (more at startup) |
| Air cooler | 180 W |
| Mixer / small motor | 500–700 W |
Common household appliance wattages
Step 3: Add it up (worked example)
Take a 3BHK that wants 3 fans (225W), 8 lights (110W), a TV (100W), Wi-Fi (35W) and the fridge (200W). That totals about 670W running together.
Step 4: Convert to inverter VA
Divide watts by 0.7, then add ~25% margin: 670 ÷ 0.7 ≈ 960VA, plus margin ≈ 1,200VA. Round up to the next size — about 1,500VA (a Microtek LUXE 1900 class unit).
Step 5: Convert to battery Ah for your target hours
| Battery | Approx. backup |
|---|---|
| 150Ah | about 2.1 hours |
| 200Ah | about 2.9 hours |
Approximate backup for a ~670W load
Don't forget startup surge
Fridges, coolers and pumps draw a brief surge several times their running wattage when they switch on. The 25% margin in Step 4 covers normal homes; if you run multiple motors, leave a little more.
Where to next
Frequently Asked Questions
Should I include the refrigerator in the load?
Only if you want it running during cuts. It adds about 200W plus a startup surge, which pushes you toward a larger inverter and a 200Ah battery.
What if I add appliances later?
Leave 20–25% headroom when you size the inverter, so a new fan or appliance doesn't tip it into overload. That margin is already built into Step 4.
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