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What size inverter and battery do I need? Simple guide for India

Add the watts you need during a power cut, divide by 0.8 for inverter VA, then size the battery for backup hours. Worked 1BHK–3BHK examples, tubular vs lithium, prices and care.

Updated · 7 min read

On this page
  1. Step 1: List what you want to run
  2. Step 2: Work out the inverter size (VA)
  3. Step 3: Work out the battery size (Ah) for your backup hours
  4. Ready-made sizes for typical homes
  5. Tubular vs flat plate vs lithium batteries
  6. Pure sine wave vs square wave inverters
  7. Solar-ready and hybrid options
  8. Battery care: make it last
  9. Installation and safety
  10. Buying checklist
  11. Frequently asked questions

Quick answer: Add up the watts of everything you want to run during a power cut, then divide by 0.8 to get the inverter size in VA — for example, 600 W ÷ 0.8 = 750 VA (buy the next size up, like 900–1100 VA). For the battery: backup hours ≈ (battery Ah × battery volts × ~0.8) ÷ load in watts. A 12 V 150 Ah battery running 300 W lasts about 4–5 hours. Choose a pure sine wave inverter and a tubular battery for most homes, or lithium (LFP) for long life and zero maintenance.

Key takeaways

  • Inverter VA decides how much you can run; battery Ah decides for how long.
  • Use BLDC fans and LED lights to double your backup time for little money.
  • Tubular batteries cost about ₹12,000–₹18,000 (150 Ah) and last 4–6 years with care; lithium costs 3–4× more but lasts 10+ years.
  • Don't run ACs, geysers, irons or induction cooktops on a normal home inverter.
  • Pure sine wave output protects fans, fridges and electronics and keeps fans quiet.

Power cuts are still common in many parts of India, especially in summer. A properly sized inverter keeps fans, lights, Wi-Fi and the TV running without wasting money on a bigger system than you need. This guide walks through the simple maths, gives ready-made sizes for typical homes, and helps you choose the right battery.

What size inverter and battery do I need? Simple guide for India Breakdown & Visual Guide

Step 1: List what you want to run

Appliance Typical watts
LED bulb 9–12 W
LED tube light 18–22 W
Ceiling fan (regular) 60–75 W
BLDC ceiling fan 28–35 W
Table / pedestal fan 40–55 W
Wi-Fi router + ONT 10–20 W
LED TV (32–43") 40–100 W
Set-top box 10–20 W
Laptop charger 45–90 W
Desktop PC + monitor 150–300 W
Mobile charger 5–20 W
Refrigerator (running; starting surge is higher) 100–250 W
Water purifier (RO) 25–60 W
Mixer grinder (short use) 500–750 W

Avoid on a normal inverter: AC (1,000–2,000 W+), geyser (2,000 W), iron (1,000 W), induction cooktop (1,500–2,000 W), microwave (1,000–1,500 W), washing machine heaters.

Step 2: Work out the inverter size (VA)

Inverter VA = total watts ÷ 0.8 (0.8 is the power factor for typical home loads). Then pick the next standard size up for safety and future additions.

Example: 4 BLDC fans (4 × 32 W = 128 W) + 6 LED bulbs (6 × 10 W = 60 W) + 2 LED tubes (40 W) + Wi-Fi (15 W) + TV (70 W) + laptop (60 W) = 373 W. 373 ÷ 0.8 = 466 VA → choose a 700–900 VA inverter.

Standard home inverter sizes: 600–700 VA, 850–900 VA, 1100 VA, 1500 VA, 2000–2500 VA (bigger ones usually use 24 V with two batteries).

Step 3: Work out the battery size (Ah) for your backup hours

Backup hours ≈ (Ah × battery voltage × 0.8) ÷ load in watts

The 0.8 allows for inverter losses and avoids draining the battery completely.

Battery Load 200 W Load 300 W Load 500 W
12 V 100 Ah ~4.8 h ~3.2 h ~1.9 h
12 V 150 Ah ~7.2 h ~4.8 h ~2.9 h
12 V 200 Ah ~9.6 h ~6.4 h ~3.8 h
2 × 12 V 150 Ah (24 V system) ~14.4 h ~9.6 h ~5.8 h

These are estimates. Real backup is a bit lower with older batteries, high temperatures and fridges that cycle on and off.

To find the battery you need: Ah = (load W × hours) ÷ (12 × 0.8) for a 12 V battery.

Example: 373 W for 4 hours → (373 × 4) ÷ 9.6 = 155 Ah → a 12 V 150–165 Ah battery.

Ready-made sizes for typical homes

Home What you run Inverter Battery Expected backup
1BHK 2 fans, 4 lights, Wi-Fi, TV 700–900 VA 1 × 12 V 150 Ah ~4–6 h
2BHK 3–4 fans, 6–8 lights, Wi-Fi, TV, laptop 900–1100 VA 1 × 12 V 150–200 Ah ~3–5 h
2BHK with fridge Above + fridge 1100–1500 VA 2 × 12 V 150 Ah (24 V) ~5–7 h
3BHK 5–6 fans, 10 lights, 2 TVs, Wi-Fi, PC 1500–2000 VA 2 × 12 V 150–200 Ah (24 V) ~4–6 h

Tip: Replacing regular fans with BLDC fans cuts each fan's load from ~70 W to ~30 W. In a 4-fan home, that's 160 W saved — often enough to double your backup time on the same battery.

Tubular vs flat plate vs lithium batteries

Price (150 Ah equivalent) Lowest ~₹12,000–₹18,000 ~₹40,000+
Typical life 2–4 years 4–6 years 10+ years (3,000+ cycles)
Best for Short, rare power cuts Frequent, long cuts — most homes Daily long cuts, solar, apartments
Maintenance Water top-up every 1–2 months Water top-up every 3–6 months None
Charging speed Slow Slow–medium Fast
Usable capacity ~50–60% ~70–80% 80–90%
Weight / space Heavy Heavy, tall Light, compact
Fumes Some during charging Some None

Lithium works best with an inverter designed or configured for lithium charging. Ask the seller to confirm compatibility.

Pure sine wave vs square wave inverters

  • Pure sine wave: clean power like the grid — fans run quiet and cool, and fridges, laptops, LED drivers and pumps are safe. Choose this.
  • Square / modified sine wave: cheaper, but causes humming in fans, more heat, and can damage sensitive electronics.

Solar-ready and hybrid options

If you plan rooftop solar later:

  • A solar inverter (PCU) or hybrid inverter can charge the battery from solar panels during the day.
  • On-grid solar under the PM Surya Ghar subsidy doesn't provide backup by itself — see PM Surya Ghar subsidy.
  • Hybrid systems combine both: grid export plus battery backup.

Battery care: make it last

  • Top up with distilled water only, up to the max mark (lead-acid). Check every 1–3 months in summer.
  • Keep the battery in a ventilated, shaded spot — never in a closed cupboard or direct sun.
  • Keep terminals clean and apply petroleum jelly to prevent corrosion.
  • Don't drain it fully often; recharge soon after long cuts.
  • If you have few power cuts, discharge it once a month to keep it healthy.
  • Don't add new loads like an iron or heater "just for a minute".

Installation and safety

  • Use proper wiring through the inverter circuit (only selected sockets and lights).
  • Use thick enough cables between inverter and battery, with secure lugs.
  • Keep children away from batteries; lead-acid batteries contain acid and release hydrogen while charging.
  • Use a stand or tray for batteries, not the bare floor.

Buying checklist

  1. ☐ Your load in watts and needed backup hours
  2. ☐ Pure sine wave inverter, right VA size
  3. ☐ Tall tubular (or lithium) battery with the right Ah
  4. ☐ Warranty: inverter 2–3 years, tubular battery 36–60 months (part free + pro-rata)
  5. ☐ Battery trolley/stand and installation included
  6. ☐ Bypass switch and overload protection
  7. ☐ Solar-ready if you may add panels later

Frequently asked questions

Which inverter is best for a 2BHK flat?

Usually a 900–1100 VA pure sine wave inverter with a 150–200 Ah tubular battery, for fans, lights, Wi-Fi and a TV.

How long will a 150 Ah battery last?

About 4–5 hours at 300 W, 7 hours at 200 W, and under 3 hours at 500 W.

Can I run a fridge on an inverter?

Yes, on a pure sine wave inverter of about 1100 VA or more. Fridges draw a surge when starting, so size up.

Can an inverter run an AC?

Not a normal home inverter. ACs need large inverters, big battery banks or solar hybrid systems.

Is lithium better than tubular for home inverters?

Lithium lasts longer and needs no maintenance, but costs several times more. Tubular is still the best value for most homes.

How do I calculate inverter VA?

Add up the watts you'll run and divide by 0.8, then choose the next standard size.

How often should I add water to an inverter battery?

Check every 1–3 months, especially in summer. Use only distilled water.