One refrigeration ton is 12,000 BTU per hour. A common DIY planning factor is 20 BTU per square foot (about one ton per 600 sq ft) for an average climate and 8 ft ceilings. Hot-humid regions often use 25–30 BTU/sq ft; cooler, shaded homes may use 15–18.
This tool scales load if ceilings are taller than 8 ft, applies ±10% for very sunny or shaded rooms, adds 600 BTU for each occupant beyond two, and can add 4,000 BTU for a kitchen—figures aligned with popular residential rules of thumb, not a Manual J.
Always confirm with a licensed HVAC contractor before buying equipment. Oversized air conditioners short-cycle and dehumidify poorly.
If you do not have a floor plan, start with the square foot calculator. A closed bedroom also needs filtration—use the CADR calculator. Backup power for a heat wave is a different job: the solar battery calculator.
How this calculation works
BTU = sq ft × BTU/sq ft, adjusted for height, sun, people, kitchen. Tons = BTU ÷ 12,000.
Calculator
Use 15–18 BTU/sq ft in cool climates, 20 for average, 25–30 in hot-humid regions (planning only).