Ton (HVAC)
The unit cooling equipment is sized in — 12,000 BTU/h of heat-removal capacity, not a unit of weight.
A "ton" of air conditioning is 12,000 BTU per hour of cooling capacity — historically, the amount of heat needed to melt one ton of ice in 24 hours. Residential equipment is sold in half-ton steps (1.5, 2, 2.5, 3, 3.5, 4, 5 tons), and a load calculation's raw BTU figure gets snapped to the nearest of those sizes rather than rounded up.
A typical 2,000 sq ft home needs about 3.5 to 5 tons of cooling depending on climate — roughly 400 to 600 sq ft per ton, with hotter climates needing more tons per square foot. Oversizing past the nearest size is a common mistake: a too-large unit cools the air quickly and shuts off before it removes enough humidity, leaving the house cold and clammy.