By Zencalcy Editorial TeamLast reviewed About us
One ton of cooling removes 12,000 BTU per hour, and the rough sizing rule is one ton for every 500 to 600 square feet of living space. Sunny exposures, extra occupants and heat-producing appliances push a room toward the smaller square footage per ton.
Air conditioner size in tons from floor area and conditions.
BTU = area × 20 + sun adjustment + 600 × extra occupants tons = BTU ÷ 12,000
The base 20 BTU per square foot is the 600 sq ft per ton rule for average conditions. Manual J load calculations account for insulation, windows and climate far more accurately than area alone; treat this as a first pass before buying.
| Symbol | Meaning |
|---|---|
| A | Conditioned floor area. |
| Q | Cooling load in BTU/hr. |
| T | Cooling capacity in tons. |
1,500 × 20 = 30,000 BTU/hr, which is 2.5 tons — the standard size for a 1,500 square foot home in a moderate climate.
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About one ton per 600 square feet in average conditions, one per 500 in hot sunny climates, and one per 700 or more in cool or well-insulated homes.
Results use standard construction estimating arithmetic: volumes from measured area and depth, unit weights from published material densities, and code-referenced spans or clearances where the page names a code. Quantities are rounded up to whole saleable units and include the stated waste allowance. These tools are planning aids, not structural design, and do not replace a licensed engineer, a local code check, or a contractor's site measurement.
Reference material used to build and check this calculator:
Last reviewed: September 2026. See how we build and check every tool on the about page.
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Content updated: September 2026