Cooling Load Rules of Thumb
Square-feet-per-ton estimating ranges by building type, for a first-pass cooling load or a sanity check on a calculated one. These are rules of thumb only — a proper ACCA Manual J load calculation is always authoritative, because floor area is just one of many factors that set the real load.
SqFt per ton by building type
| Building type | SqFt / ton | BTU / sqft | Note |
|---|---|---|---|
| Residential | 400–600 | 20–30 | Modern tight/efficient homes run much leaner — 700–1,500+ sqft/ton; 400–600 often oversizes. |
| Office | 250–400 | 30–48 | Efficient, well-glazed offices reach 500–600; lower end = high occupancy or glass. |
| Retail | 250–400 | 30–48 | — |
| Restaurant dining | 100–250 | 48–120 | High internal + latent load; kitchens far lower — size by cooking equipment, not area. |
| School / classroom | 200–250 | 48–60 | Under-sourced; indicative only — high occupancy and ventilation code drive it below office. |
| Server / IT room | 150–300 | 40–80 | Dedicated data centers: size by kW load, not floor area. |
| Assembly (worship / theater) | 105–250 | 48–112 | Wide spread by occupancy. |
Use it to check, not to size
The right way to use this table is as a reasonableness check. Run a load calculation or a tonnage estimate, then compare it against the rule of thumb for the building type — if a 2,000 sqft office comes out at 10 tons, the ~250–400 sqft/ton range flags it as far too big. What the ranges cannot do is size the equipment, because they ignore everything that actually drives load: glass, insulation, air-tightness, occupancy, ventilation, and internal gains.
The spread within each type is real. An efficient, well-shaded office can hit 500–600 sqft/ton while a glassy, densely-occupied one needs 250; a restaurant kitchen has so much cooking and makeup-air load that area barely applies. Newer construction trends leaner than the old numbers, so treat the low end of the residential range as a ceiling, not a target.
Common questions
How many square feet per ton of air conditioning?
It depends heavily on the building. As a rough planning figure, residential runs 400–600 sqft/ton, offices and retail 250–400, and high-load spaces like restaurants 100–250. But these are only starting points — a modern tight, well-insulated home can reach 1,000–1,500 sqft/ton, so the old rules oversize it. A Manual J calculation is the only reliable way to size equipment.
Why can’t I just size AC by square footage?
Because floor area is only one of many factors. Glazing area and orientation, insulation levels, air-tightness, ceiling height, occupancy, ventilation requirements, and internal loads from lighting, plug loads, kitchens, or IT equipment can each move the real load by a large margin — two identical-footprint buildings can differ by 2× or more. Rules of thumb are for a first pass and a sanity check, not for equipment selection.
What is a good BTU per square foot for cooling?
Roughly 20–30 BTU/sqft for residential, 30–48 for offices and retail, and higher for dense or high-load spaces — but the same caveats apply. Since 12,000 BTU equals one ton, 500 sqft/ton works out to 24 BTU/sqft and 300 sqft/ton to 40 BTU/sqft.
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