AC BTU Calculator
An oversized AC unit short-cycles, wastes energy, and fails to dehumidify properly. An undersized unit runs constantly without reaching the set temperature. This calculator determines the correct BTU capacity for your room by accounting for area, ceiling height, insulation quality, climate zone, and sun exposure.
The calculation starts with a base of 20 BTU per square foot, then applies multipliers for real-world conditions. Tall ceilings increase the air volume to condition. Poor insulation lets heat transfer faster through walls and ceilings. Heavy sun exposure adds solar heat gain through windows. Hot climates require more cooling capacity.
AC systems are sized in tons, where 1 ton equals 12,000 BTU/hr. Standard residential systems come in 1.5, 2, 2.5, 3, 3.5, 4, and 5 ton sizes. Mini-split systems are available in smaller increments from 9,000 to 36,000 BTU. Always round up to the nearest available size rather than rounding down.
Heating BTU requirements differ from cooling. In cold climates, heating demand can be 20% higher than cooling because the temperature differential is larger (heating from 0°F to 68°F is a bigger jump than cooling from 95°F to 75°F). This calculator adjusts the heating estimate based on your climate zone.