To convert BTUs to tons, find the BTU capacity of the air conditioner, and divide the BTUs by 12,000. Twelve thousand BTUs equals the amount of heat removed by an air conditioner that would melt 1 ton of ice in 24 hours, which is called the chiller refrigeration ton, according to The Engineering Toolbox.

**Find the BTU capacity**On the tag or packaging, find the BTU rating of the air conditioner. The number is expressed in thousands, such as 6,000 BTU or 15,000 BTU.

**Divide the BTUs by 12,000**Using a calculator, divide the unit's BTU rating by 12,000 to arrive at the chiller refrigeration ton capacity. The equation may yield a fraction. For instance, a 6,000-BTU window air conditioner equals 1/2 ton of cooling capacity.

**Apply the tonnage to the space**An old rule of thumb stipulated that 1 ton of air conditioning should cool 400 square feet of living space. However, many air conditioners are too large for the site, which results in high humidity and wasted energy. The current thinking, according to Green Building Advisor, is 1 ton per 1,000 square feet of space, with some adjustments based on ceiling height, climate, number of windows and other variables.