Buy undersized and the AC runs forever without cooling; oversized and it short-cycles, wasting money and dehumidifying poorly. Tonnage is the whole game — here's the chart that decides it.
The base chart
100 sq ft (10×10): 1 ton. 100-150 sq ft (12×12): 1.5 ton. 150-200 sq ft (15×15): 1.5-2 ton. 200-250 sq ft: 2 ton. This assumes standard 8-9ft ceilings and moderate insulation.
The adjustment factors
Add capacity for: top-floor rooms (+0.5 ton), west/south-facing walls with afternoon sun (+0.25-0.5 ton), large windows (+0.25), kitchens attached (+0.25), more than 3 regular occupants (+0.25 per 2 people), and high ceilings above 10ft.
The cost of getting it wrong
Undersized: runs at 100% forever, never reaches set temperature, highest possible bill, compressor dies early. Oversized: cools fast then short-cycles — poor dehumidification (clammy cool), more on/off wear, higher upfront cost. Right-sized is genuinely optimal both ways.
| Room size | Normal conditions | Hot conditions (top floor/west) |
|---|---|---|
| 10×10 (100 sq ft) | 1 ton | 1.2-1.5 ton |
| 12×12 (144 sq ft) | 1.5 ton | 1.5-2 ton |
| 15×15 (225 sq ft) | 2 ton | 2+ ton |
| 18×18 (324 sq ft) | 2 ton × 2 units | 2.5-3 ton total |
The verdict
The 12×12 Indian bedroom — the most common case — wants a 1.5-ton 5-star inverter, and no dealer upsell to 2-ton. Measure your room, add the adjustment factors, buy the number.
Our picks
Convertible modes cover mild days
The default answer for the default room
Big-room cooling with inverter savings
FAQs
Can a 1-ton cool a 12×12 room?
In a hill station, maybe. In Delhi May on the top floor — never. It'll run at 100% forever, feel weak, and die young. Match tonnage honestly.
Does a bigger AC cool faster?
Yes but then it short-cycles — cool-fast-humid-clammy. 'Cool' is temperature AND humidity; right-sizing handles both.