What Tonnage AC Do You Need for Your Room Size?

Yes. A 100 sq ft room needs about 0.75 ton and a 120 sq ft room about 0.9 ton, so a true 1 ton covers both. Check that the unit is rated near 3,500 W — Daikin's ATKL35XV (3,520 W), Hitachi's RAS.V512PCDIST (3,516 W) and Lloyd's GLS12I3AGGSR (3,500 W) are; some 1 ton-class units are rated 3,100-3,350 W.

The exception is a 120 sq ft top-floor room with afternoon sun, which calculates to about 1.2 ton. There a 1.5 ton is right.

Yes, on a middle floor. 150 sq ft needs about 1.1 ton and 180 sq ft about 1.35 ton. For 180 sq ft, pick a unit rated at 5,000 W or more — LG's AS-Q19MNXE (5,300 W), Panasonic's HU18CKY5XFMH (5,280 W) or Haier's HSU19K (5,460 W) — rather than one rated nearer 4,750 W.

On a sunny top floor, 180 sq ft calculates to about 1.85 ton, and a 2 ton is the correct buy.

200 sq ft: usually no. A middle-floor 200 sq ft room is a 1.5 ton load. It needs 2 ton only on a top floor, with strong afternoon sun, or with several people regularly in it.

250 sq ft: yes, and a true 2 ton rated close to 7,000 W — Daikin's FTKL71XV or Hitachi's Sumo RAS.Y324PCDISL. Units rated 6,100-6,300 W suit about 230-240 sq ft.

300 sq ft: about 2.25 ton, more than one 2 ton AC delivers. Two units — two 1.5 ton, or a 2 ton plus a 1 ton — cool evenly and give you a backup.

• Top floor, roof slab above: add about 20%.
• West or south-facing with large windows: add about 15%.
• 12 ft ceiling instead of 10 ft: add about 20%.
• Extreme dry heat (Delhi, Rajasthan, Nagpur, UP): add about 10%.
• Each person beyond two: add about 600 BTU/h.
• Room open to a kitchen, or with a desktop PC or server running: add more.