Home & Power
What Size AC Do I Need? Tonnage by Room Size
The 120 sq ft rule, adjustments for top floors and people, a tonnage chart by room size, and what to look for in inverter and star ratings.
By Team Vind · Updated · 5 min read
Buy an AC that's too small and it runs flat out all afternoon without ever cooling the room. Buy one too big and you pay more upfront, and a fixed-speed model leaves the room cold but clammy. The right size depends mainly on floor area, then on sun, ceiling height and people.
The quick rule
Tons ≈ room area (sq ft) ÷ 120, for a 10 ft ceiling
Then adjust:
- Top floor, west-facing or big windows: add about 20%.
- Shaded room on a lower floor: take off about 10%.
- More than two people using the room regularly: add 0.1 ton for each extra person.
- Kitchen or open kitchen: add about 0.5 ton.
- Higher ceiling: scale by height ÷ 10.
Example: a 12 × 14 ft bedroom on the top floor, 3 people: 168 ÷ 120 × 1.2 + 0.1 = 1.78 ton, so a 2 ton AC.
AC size chart by room
| Room | Area | Shaded / lower floor | Normal | Top floor / west-facing |
|---|---|---|---|---|
| 10 × 10 ft | 100 sq ft | 0.75 ton | 1 ton | 1 ton |
| 10 × 12 ft | 120 sq ft | 1 ton | 1 ton | 1.5 ton |
| 12 × 12 ft | 144 sq ft | 1.5 ton | 1.5 ton | 1.5 ton |
| 12 × 14 ft | 168 sq ft | 1.5 ton | 1.5 ton | 2 ton |
| 14 × 16 ft | 224 sq ft | 2 ton | 2 ton | 2.5 ton |
| 16 × 20 ft | 320 sq ft | 2.5 ton | 3 ton | 3 ton |
Try it: AC Tonnage Calculator
A 1.5 Ton AC Suits This Room
Usual AC size by room area
| Room area | AC size |
|---|---|
| Up to 90 sq ft | 0.75 ton |
| 90–125 sq ft | 1 ton |
| 125–180 sq ft | 1.5 ton |
| 180–240 sq ft | 2 ton |
| 240–300 sq ft | 2.5 ton |
| 300–360 sq ft | 3 ton |
What a "ton" means
A ton is a measure of cooling, not weight or electricity: 1 ton = 12,000 BTU per hour = 3.5 kW of heat removed. The name comes from the cooling of one ton of ice melting in a day. A 1.5 ton inverter AC typically uses about 1–1.5 kW of electricity at full power, and much less once the room is cool.
Inverter or fixed speed? Stars?
- Inverter ACs slow down instead of switching off, so they use less power over a long summer and cope better with a slight oversize. They're the standard choice today.
- Star rating (BEE): a 5-star AC uses roughly 20–30% less electricity than a 3-star. If you run it 8+ hours a day for several months, the extra price usually pays back in a few years.
- Check the yearly units printed on the BEE label and multiply by your tariff to compare running costs.
Want to know what it costs to run? Read how your electricity bill is calculated or use the electricity bill calculator.
Frequently asked questions
Which AC is best for a 12 × 12 room?
1.5 ton. 144 sq ft needs about 1.2 ton in a normal room and more on a top floor, so 1.5 ton is the usual choice.
Is 1 ton AC enough for 150 sq ft?
Only in a shaded, lower-floor room. In most cases 150 sq ft needs a 1.5 ton AC.
How many units does a 1.5 ton AC use per hour?
About 1 to 1.5 units (kWh) per hour at full power for a 5-star inverter model, less once the room is cool.
Is a bigger AC better?
Not beyond what the room needs. It costs more and, if fixed-speed, cycles on and off and removes less humidity.
Sources
- Bureau of Energy Efficiency: star labelling for room air conditioners
- Ministry of Power / BEE: default 24 °C temperature setting for ACs
Last reviewed: 10 October 2026