Well first off, tonnage is measured in the amount of BTUs (British Thermal Units) the air conditioning system is capable of removing. 1 ton is equal to 12,000 BTUs. So to make this simple, if your unit is a newer unit, say 20 years or newer, there will be a number in your model number divisible by 12 that represents the number of BTUs in thousands. Using this method, every multiple of 12 (12,000 BTUs) is equal to 1 ton of air. Both the condenser and air handler have a sticker or plate on them that shows the model number and serial number. Most all the time you can determine your tonnage this way. There are exceptions with certain brands and models.
Listed below are the most common BTU numbers with their resulting tonnage.
18 (18,000 BTUs) = 1.5 ton
24 (24,000 BTUs) = 2 ton
30 (30,000 BTUs) = 2.5 ton
36 (36,000 BTUs) = 3 ton
42 (42,000 BTUs) = 3.5 ton
48 (48,000 BTUs) = 4 ton
60 (60,000 BTUs) = 5 tonTags: size, Tonnage