A quick AC sizing estimate uses square feet per ton — area divided by a rule-of-thumb sqft/ton gives the tonnage. One ton = 12,000 BTU/hr of cooling.
The example
2,000 sq ft, 500 sqft/ton.
| A | B | |
|---|---|---|
| 1 | Item | Value |
| 2 | 2000 / 500 | — |
| 3 | Tonnage | → 4 tons |
The formula
The formula:
How it works
How it works:
- Divide conditioned area by the sqft per ton rule for your climate (often 400–600).
- Convert to BTU/hr: tons × 12,000.
- ROUNDUP to the nearest half-ton equipment size sold.
- A rule-of-thumb is a starting point — a Manual J load calc is the real sizing.
Rule-of-thumb sizing is for ballpark quotes, not installs. Square-feet-per-ton ignores insulation, windows, orientation, ceiling height, and infiltration — the things a proper Manual J load calculation accounts for. Oversizing short-cycles and fails to dehumidify; undersizing never keeps up. Use sqft/ton to sanity-check and quote fast, then do the real load calc before specifying equipment. This is illustrative, not an engineering sizing.
Try it: interactive demo
Square feet and sqft per ton.
Variations
BTU per hour
Tons × 12,000:
Round to equipment size
Half-ton steps:
Sqft per ton from a unit
Back out the rule:
Pitfalls & errors
Rule of thumb. Sqft/ton is a quote tool, not a sizing — do Manual J.
1 ton = 12,000 BTU/hr. Use the constant for BTU.
Round to sizes sold. Equipment comes in half-ton steps.
Practice workbook
Frequently asked questions
How do I estimate AC tonnage in Excel?
How do I get BTU per hour?
Is sqft per ton accurate?
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