How to Size an Inverter & Battery for Your Home

The most common reason an inverter system disappoints is simple: it was the wrong size. Too small and it trips or dies within minutes; too large and you have paid for capacity you never use. Getting the sizing right is the difference between a system that quietly powers your home for years and one that frustrates you daily. This guide shows you exactly how to size an inverter and battery for your home in Nigeria.

Step 1: List your appliances and their wattage

Write down every appliance you want to run during an outage and its power rating in watts. Typical values:

• LED bulb: 5–15W each
• Ceiling/standing fan: 60–75W
• Television: 60–150W
• Decoder / Wi-Fi router: 15–30W
• Refrigerator: 150–250W running (with a higher surge at startup)
• Pumping machine: 750W–1,500W (high startup surge)
• Laptop / phone chargers: 30–90W

Step 2: Add up your total running load

Sum the wattage of everything you might run at the same time. This peak figure is your running load. Then account for surge: motors in fridges, freezers and pumping machines briefly draw two to three times their running wattage when they switch on, so your inverter must handle that spike.

Step 3: Choose your inverter capacity

Inverters are rated in kVA. Convert your total watts to kVA (divide watts by about 0.8) and add headroom for surges and future appliances. As a practical guide for Nigerian homes:

• 1–1.5kVA — lights, fans, TV, decoder and chargers for a small flat.
• 2.5–3.5kVA — the above plus a fridge and more rooms.
• 5kVA and above — larger homes with fridge, freezer, pumping machine and some heavier loads.

Never load an inverter to 100% of its rating — sizing with headroom extends its life.

Step 4: Size your battery bank for backup time

Your batteries decide how long the system runs. To size them, multiply your average load (in watts) by the number of backup hours you want, then match that to battery capacity (Ah) and system voltage (12V, 24V or 48V), allowing for the battery’s usable depth of discharge. Lithium batteries allow deeper, safer discharge than tubular, so you get more usable energy from the same rating. The higher your desired backup hours and load, the bigger the battery bank.

Step 5: Match voltage and balance the system

The inverter, battery bank voltage and (if fitted) solar array must all match. A mismatched system underperforms or fails. This is where a professional design matters — balancing inverter capacity, battery voltage and panel wattage so everything works together safely.

Let us size it for you

Sizing involves real numbers, surge factors and battery chemistry — and getting it wrong is expensive. Battery Joint has sized and installed systems for over 700 homes and businesses across Nigeria since 2012. Send us your appliance list and target backup hours and we will design the right system. Request a free assessment or browse our inverters and batteries.

Frequently asked questions

What size inverter do I need to run a fridge?

A fridge draws 150–250W running but surges higher at startup, so it needs a pure sine wave inverter sized for that surge — commonly 1.5kVA or larger depending on what else you run alongside it.

How do I calculate battery backup time?

Multiply your average load in watts by the hours of backup you want, then size the battery bank’s usable capacity to match. Larger battery capacity and higher voltage give longer runtime.

What does kVA mean on an inverter?

kVA (kilovolt-amperes) is the inverter’s power capacity. To estimate the watts it can handle, multiply the kVA by roughly 0.8. Always size with headroom above your peak load.

Is it better to oversize or undersize?

Neither extreme is ideal. Undersizing causes trips and early failure; heavy oversizing wastes money. The goal is the right size with sensible headroom for surges and a little future growth.