calcs.homes
calcs.homes
Enter your home's conditioned area, climate, ceiling height, and insulation level, and this AC tonnage calculator estimates the system size in tons and BTU per hour.
Estimate only — right-sizing central air needs a Manual J calculation done for your specific house.
One ton of cooling equals 12,000 BTU per hour. We multiply your conditioned area by a climate factor — roughly 20 BTU/sq ft in mild-summer regions up to 30 in the hot South — then adjust for ceiling height and how tight the house is, and divide by 12,000. The result is rounded to the nearest half ton, because residential equipment is only made in those steps.
Rules of thumb are a starting point, not a spec. A contractor should run a Manual J load calculation that measures your actual window area and orientation, insulation R-values, infiltration, and duct losses. Oversized central air is a common and expensive mistake: it cycles on and off, wears out sooner, and leaves the house cold but humid.
Roughly 2.5 to 3.5 tons depending on climate, insulation, and ceiling height — about 3 tons for an average home in a warm climate.
A common range is 400 to 600 sq ft per ton. Hot climates and leaky homes sit near the low end; mild climates and tight homes near the high end.
Residential condensers are built in 0.5-ton increments (2, 2.5, 3 tons and so on), so any calculated load has to be matched to the nearest real unit.