How to calculate AC tonnage for your Home or Office


Summers setting in, and it’s time to bring out those AC’s, and a lot of us will be out looking for new AC’s this season.. Shopping for the right kind of air conditioner can be quite confusing, and a lot of times we can be misled into buying a larger unit than required or worse than that, buying something which is too small for our room!
It is important to have some idea about how to calculate the AC capacity that you require for your room… which depends not only on the size of the room but also on the size of the windows, which direction they face, number of people who occupy it, the insulation of the room (is it on the top floor or in the basement) even the wattage of equipment in the room influences the required AC capacity (more relevant for offices).

The most basic thumb rule to get started is to calculate the volume of your room in feet and divide it by 1000, this will give you the required capacity in TR (tons). So a 10 foot by 10 foot room which is 10 feet high will need a one ton AC (10’x10’x10’ = 1000 Cu.ft. / 1000 = 1 ton).

But to add some precision to this calculation do the following:

Measure the dimensions of your room.
Identify the orientation of your windows and measure their sizes (don’t add up the window sizes as a north facing window impacts the calculation different from a south facing window)

Follow the links below and use the AC tonnage calculator provided by companies like Bluestar and LG to get a the required tonnage for your room (more calculators can be found online)

After this let’s understand the units. One ton (TR) of refrigeration refers to the heat extraction capacity of the unit, it’s an American unit and equates to the amount of energy required to melt one short ton of ice (about 907 KG or 2000 pounds). This is equivalent to 12000 BTU/h (British thermal unit), beware of products that claim to be a one ton unit but have a cooling capacity of less than 12000 BTU. Finally we need to check the power consumed by the unit in watts and the star rating which is based on the EER (energy efficiency ratio). If we convert the cooling capacity to watts (1 ton = 12000 BTU = 3517 watts) and then divide it by the power consumed to achieve this we get the EER, the higher the better (this shouldn’t ever be below 2.3 and should be around 3.5 for a 5-star rating).

So to summarize:
Calculate the cooling capacity (in TR) based on your room requirements
Check the cooling capacity (in TONS as well as BTU then convert it to watts)
Check the power consumed.
Check the BEE rating. (verify by dividing cooling capacity by Power consumed)