BTU is the way that we measure the cooling capacity of an air conditioner. It refers to British Thermal units. The higher the BTUs, the higher the cooling capacity of the air conditioner.
To get technical, each BTU equals how much air (measured in cubic feet) that an air conditioner could cool in one hour.
As an example, let’s say that you have a 10000 BTU air conditioner. That means that it can be expected to cool down 10000 cubic feet of air each hour.
What does this mean in terms of square footage?
A 10000 BTU air conditioner should be able to cool 500 square feet. (Of course, a portable ac unit is not nearly as efficient as a central air conditioner. A portable unit that is 10000 BTUs will only cool about 200-300 square feet,)
There are other issues to consider, however. In particular, the amount of insulation in your room can impact the cooling capability of your air conditioner. A hot kitchen can also increase the amount of cooling that you need.
So run the numbers and see what size air conditioner is best for your home. You might want to buy one that is slightly larger than the recommended size. This will ensure that you stay cool, but it won’t break the bank when you receive your energy bill.