Most rooms need about 20 BTU per square foot in moderate climates and 25–30 in hot climates. This calculator applies the full set of load adjustments — ceiling, sun, occupants, windows, insulation — and gives you BTU/hr first, tonnage second.
Estimate only — confirm equipment sizing with a Manual J load calculation by a licensed contractor.
| Cooling load | — |
| Thermal power | — |
| Floor area | — |
| Duct airflow needed | — |
Cooling capacity is measured in BTU per hour. Start from floor area, then adjust for what makes a room harder or easier to cool:
India note: single-room splits carry harsher solar loads — plan on roughly 90–120 BTU/sq ft per room, which is why “1 ton per 100 sq ft” is the local rule of thumb.
| BTU/hr | Tons | Typical use |
|---|---|---|
| 5,000 | 0.42 | Small bedroom window unit |
| 9,000 | 0.75 | Mini-split bedroom zone / 0.75T split |
| 12,000 | 1.0 | 1 ton split AC |
| 18,000 | 1.5 | 1.5 ton split — India's most common size |
| 24,000 | 2.0 | 2 ton split / small central system |
| 36,000 | 3.0 | 3 ton central AC (~1,500 sq ft US home) |
| 60,000 | 5.0 | 5 ton central AC (~2,500 sq ft US home) |
A British Thermal Unit is the amount of heat needed to raise one pound of water by 1°F, measured near water’s point of maximum density (about 39°F) at standard atmospheric pressure — roughly 1,055 joules. Cooling capacity is quoted in BTU per hour: 12,000 BTU/hr = 1 ton. Convert any value with the BTU → tons converter.
The common baseline is 20 BTU per square foot in a moderate climate, rising to 25–30 BTU/sq ft in hot climates like Arizona, Texas or most of India. Ceiling height, sun exposure and insulation then adjust the figure.
1 refrigeration ton equals exactly 12,000 BTU per hour. A 2-ton unit is 24,000 BTU/hr, a 3-ton unit is 36,000 BTU/hr.
A 12×12 room is 144 sq ft. At 20 BTU/sq ft that's roughly 2,900 BTU in a moderate climate, but a sunny, top-floor Indian bedroom can need 14,000+ BTU — which is why a 1 or 1.5 ton split AC is the usual answer there.
BTU estimates follow ACCA Manual J load principles (ANSI/ACCA 2) and the ASHRAE Handbook — Fundamentals — ACCA, ASHRAE. See our full methodology.