How to calculate the air conditioning requirement of any room?

Many websites and buying guides give a detailed calculation of cooling requirement of any room. However there are so many factors which determine the exact value of Air conditioning you need for a room. Any more or any less will lead to a lot of wastages.

Basic formula

  • 20 BTU per sq feet (many people take it as 25)
  • 1 Ton = 12000 BTU per hour
  • One person requires 600 BTU per hour of cooling in a room
  • Sq Feet is calculated by multiplying length and width of a room

What is BTU

BTU stands for British Thermal Unit.

One ton of cooling is defined as 12000 BTU per hour. It is also defined as the amount of cooling need to freeze one ton of water to ice in 24 hours.


Let us take the example of a 300 sq ft an average size of a bedroom in India.

300 sq ft x 20 = 6000 BTU

1 ton = 12000 BTU per hour

So roughly you need 0.5 Ton AC to cool the room.

600 BTU per person so for two persons in the room we need 1000 BTU.

If the out side of the room is sunny without any shade add 1000 BTU. If insulation is inadequate add another 2000 BTU and for a standard ceiling size add another 1000 BTU. That totals to 4000 BTU.

So the total requirement of a bedroom comes to 6000+4000+1000 = 11000 BTU

This calculation means we need 1 Ton cooling capacity for the bedroom. So anything between a 1 ton to 1.5 ton AC unit should suffice.

AC is a complex piece of technology

To get the best out of your air conditioner you also need to pay attention to the following points.

  • Star rating of an AC is the most critical thing to watch. A higher star rated AC will cool the room with lesser electricity and a lower star rated AC.
  • Clean the air filter regularly. It is a simple non tech job but will save a lot in terms of electricity consumption.
  • Remember, you cannot ignore the laws to thermodynamics. Check the outside temperature and set the AC at 5 degrees cooler. This is the most efficient settings.
  • The AC consumes lot of power. So make sure that the wiring is of correct gauge and switches are of high quality.
  • Do not forget a good quality stabiliser.

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