Work out air conditioner sizing instantly with clear inputs, formula shown and shareable results.
Air conditioner selection starts from an area-based load, then adds the gains the area rate ignores: about 600 BTU/h for every occupant beyond two and roughly 900 BTU/h for each sun-exposed window. The raw load is rounded up to the nearest half ton because that is how equipment is actually catalogued, and 400 CFM per ton gives the matching indoor airflow.
Sizing load
BTU/h = area x rate + max(occupants - 2, 0) x 600 + windows x 900
Nominal size
tons = ceil(BTU/h / 12000 x 2) / 2; airflow = tons x 400 CFM
BTU/h = area x rate + max(occupants - 2, 0) x 600 + windows x 900. Air conditioner selection starts from an area-based load, then adds the gains the area rate ignores: about 600 BTU/h for every occupant beyond two and roughly 900 BTU/h for each sun-exposed window.
It is the standard design airflow for comfort cooling. Lower airflow increases dehumidification but risks coil freezing; higher airflow reduces latent capacity.
This calculator takes 4 inputs: Floor area, Climate base rate, Regular occupants, Sun-exposed windows. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.