How to Choose the Right Inverter Size for Your Home

Most people get this wrong. They walk into a shop, ask for ‘a good inverter,’ and come home with something either too weak to handle their load or too large for their power cuts.

This guide fixes that. By the end, you’ll know exactly which size inverter you need, before you speak to any salesperson.

Step 1: Calculate Your Load in Watts

Write down every appliance you want to run during a power cut. Then note the wattage of each.

A typical 2BHK in India runs something like this during a power cut:

• 4 ceiling fans – 75W each = 300W
• 8 LED lights – 10W each = 80W
• 1 television – 80W
• 1 WiFi router – 10W
• 1 refrigerator (if needed) – 150W

Total: approximately 620W. That is your load.

Step 2: Convert Watts to VA (the inverter’s unit)

Inverters are rated in VA (volt-amperes), not watts. To convert your watt load to VA, divide by 0.8 – the standard power factor for home inverters.

620W divided by 0.8 = 775 VA

Now add a 20% safety buffer so your inverter does not run at 100% capacity all the time:

775 VA × 1.2 = 930 VA

You need a 1000 VA inverter. The Invertek Rapid+ 1050/12V at 800VA or Rapid+ 1250/12V at 1050VA is your range.

Step 3: Add an AC? Change Your Size

A 1.5-ton air conditioner uses 1500-1800W alone. If you want to run an AC during a power cut, your entire sizing calculation changes.

1 AC (1.5T) + basic 2BHK load = approximately 2,100W.

2100W / 0.8 × 1.2 = 3,150 VA

That puts you in the Rapid+ 3500/24V category – a 24V dual-battery system.

Important: Never try to run an AC on an inverter sized for basic home loads. It will trip or damage the unit within weeks.

Step 4: Choose Your Battery Size Based on Backup Time

The inverter controls the power. The battery controls how long you get it.

The formula is straightforward:

Battery capacity (Ah) = (Load in watts × Backup hours) / Battery voltage / efficiency

For a 620W load on a 12V system with 80% efficiency, wanting 4 hours of backup:

(620 × 4) / 12 / 0.8 = 258 Ah

A 150Ah battery gives you approximately 2.3 hours at 620W. Two 150Ah batteries give you close to 4.5 hours.

If you want longer backup without adding battery weight, consider a lithium battery. A 100Ah LiFePO4 battery delivers the same usable energy as a 150Ah lead-acid because lithium allows 80–90% depth of discharge versus 40–50% for lead-acid.

Common Sizing Mistakes to Avoid

• Buying by price, not by load: the cheapest inverter for your home may be the wrong VA for your load
• Forgetting future appliances: if you plan to add a washing machine or extra AC in the next two years, size up now
• Matching a lithium-incompatible inverter with a lithium battery: always confirm lithium compatibility before buying
• Ignoring the charging current: during long outages, a high charging current (20A like Invertek Rapid+) restores backup faster

What Invertek’s Load Calculator Does for You

If maths is not your thing, Invertek provides a free UPS Finder tool that does this calculation for you. Enter your appliances and it recommends the right model directly.

Every Invertek inverter comes with a 36-month warranty and 100+ authorised service partners across India, so the recommendation you get is backed by real support, not just a sales pitch.