Reference

AC tonnage by room size

Room size against air conditioner size, on both rules of thumb at once — Indian and Gulf retail guidance beside American whole-home guidance. They differ by a factor of four, and almost every chart prints one column without saying which.

Written againstISHRAEASHRAEChecked 29 August 2026

There are two charts, not one

Indian and Gulf retail guidance puts one ton of cooling on about 120 square feet. American whole-home guidance puts it on 400 to 600. That is roughly four times, and it is not that one of them is wrong.

An uninsulated, single-glazed room at a 45 °C design ambient loses the fight far faster than an insulated house at 32 °C. And the two figures answer different questions: the Indian one sizes a single room with a split unit, the American one averages a whole dwelling on ducted central cooling, including spaces that barely need it.

So a reader who lands on the wrong chart for their building buys a machine four times the wrong size. Both columns are here, with the rate each was computed at named in the heading.

Room size against machine size

Cooling load and recommended machine size for a room, on both rules of thumb
Roomsq ft	Roomm²	Hot, uninsulatedBTU/h	Machineton	Moderate, insulatedBTU/h	Machineton
80	7.4	8000	1.0	1920	0.5
100	9.3	10000	1.0	2400	0.5
120	11.1	12000	1.0	2880	0.5
150	13.9	15000	1.5	3600	0.5
180	16.7	18000	1.5	4320	0.5
200	18.6	20000	2.0	4800	0.5
250	23.2	25000	2.5	6000	0.5
300	27.9	30000	2.5	7200	1.0
400	37.2	40000	3.5	9600	1.0
500	46.5	50000	4.5	12000	1.0

Assumes a ten-foot ceiling, two occupants, no direct roof above and no strong afternoon sun — each of which adds. Tonnage rounds up to the half tons machines are sold in, which is why the ratio between the two tonnage columns jumps about while the BTU columns hold a constant four to one. Read the BTU columns to compare the rules; read the tonnage columns to buy.

What a ton actually is

A ton of refrigeration is the cooling a ton of ice does as it melts over a day, which is where the name comes from and why it has nothing to do with weight. It is defined as 12 000 BTU per hour. The kilowatt column follows from that definition rather than being a separate measurement, so the three columns cannot disagree.

Air conditioner capacity in tons, BTU per hour and kilowatts
Capacityton	CoolingBTU/h	CoolingkW
0.75	9000	2.64
1	12000	3.52
1.5	18000	5.28
2	24000	7.03
2.5	30000	8.79
3	36000	10.55
4	48000	14.07
5	60000	17.58

These are cooling capacities, not electrical consumption. What a machine draws from the socket depends on its efficiency — the star rating or ISEER — and is a fraction of the cooling it delivers.

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