How to Calculate Backup Power Requirements for Your Home or Office

Why Proper Sizing Matters

One of the biggest mistakes buyers make is choosing an undersized or oversized backup system. Proper sizing ensures better performance, longer battery life, and cost savings.

Step 1: List Essential Loads

Identify appliances you want during power cuts. Typical wattages: LED Lights (10–20W), Fans (60–80W), Wi-Fi Router (10W), Laptop (60W), Refrigerator (150–300W). List everything that must run during an outage.

Step 2: Calculate Total Load

Add the wattage of all devices expected to run simultaneously. For example: 4 fans (320W) + 6 lights (90W) + Router (10W) + TV (120W) = 540W total load.

Step 3: Estimate Backup Time and Battery Capacity

If you need 4 hours of backup: 540W × 4 = 2160Wh (2.16kWh). For lithium batteries, 2.5–3kWh usable storage would comfortably support this load. For lead-acid, a higher Ah rating is required due to lower usable depth of discharge.

Common Mistakes to Avoid

Watch out for ignoring surge loads, adding heavy appliances later without recalculating, using local low-quality batteries, and not checking inverter compatibility. Always keep 20–25% extra capacity for future load expansion.