AC Tonnage Calculator
Estimate what size (tonnage) air conditioner you need based on the square footage of the space.
What this calculator does
This tool gives a rough estimate of the air conditioner tonnage (cooling capacity) recommended for a room or home based on its square footage and local climate.
The formula
Total cooling load (BTU per hour) = area × a BTU-per-square-foot factor that varies by climate (roughly 20 for mild climates up to 30 for hot climates), adjusted slightly upward for ceilings taller than 8 feet. One ton of air conditioning equals 12,000 BTU/hr, so tonnage = total BTU ÷ 12,000.
This is a simplified rule-of-thumb estimate for general planning. A proper HVAC load calculation (Manual J) also accounts for insulation, windows, orientation, and occupancy, and should be used for final equipment sizing by a licensed contractor.