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Square Feet per Ton (Cooling Density) Calculator

Divide the floor area by the cooling capacity to see how hard a system is sized. It is a quick sanity check — not a way to choose equipment.

Method reviewed October 26, 2026. Version 1.0.0. How it works

Your inputs

Unit system
Capacity entered as

Nominal tons, from the model number or the AHRI rating. 12,000 BTU/h = 1 ton.

Building

For homes the result is compared with published Manual J studies. No comparison is given for other buildings.

Result

Possibly oversized

Floor area per ton
667ft²
Cooling capacity per square foot
18BTU/h·ft²

3 tons for 2,000 ft² is 667 ft² per ton (18 BTU/h per ft²).

  • Below 1,000 ft² per ton. In a published set of 40 Manual J calculations for homes the average was about 1,431 ft² per ton and most were above 1,000. A room-by-room load calculation is the way to confirm.
Cooling capacity per square foot
5.28W/ft²
Capacity
3tons
Show the working
  1. Tons = BTU/h ÷ 12,000
    36,000 ÷ 12,000 = 3 tons
  2. Square feet per ton = area ÷ tons
    2,000 ÷ 3 = 667 ft²/ton
  3. BTU/h per ft² and W per ft²
    36,000 ÷ 2,000 = 18 BTU/h·ft²; × 0.29307 = 5.28 W/ft²

The numbers

  • Tons = BTU/h ÷ 12,000
  • Square feet per ton = conditioned floor area ÷ tons
  • Cooling density = BTU/h ÷ floor area, also shown in watts per square foot (1 BTU/h = 0.293 W)

A lower square-feet-per-ton figure means more cooling per square foot.

What studies of homes find

A long-standing rule of thumb sizes homes at 400–600 ft² per ton. Allison Bailes, writing on the ACCA blog, reported 40 Manual J load calculations that averaged about 1,431 ft² per ton, with most above 1,000. A figure well under 1,000 ft² per ton for a house therefore suggests the system may be oversized — or that the house has unusual loads worth checking.

Oversized air conditioners run in short bursts, remove less moisture and wear their parts faster. The U.S. Department of Energy also warns that sizing by rules of thumb tends to oversize systems.

Why it is not a sizing method

Two houses with the same floor area can need very different equipment because of climate, insulation, window area and orientation, air leakage and occupancy. Use a room-by-room load calculation to size a system, and use this tool only to see whether a proposed or existing size is in a plausible range. No comparison range is given for commercial buildings, whose loads vary even more.

Worked example

These are the example values the calculator opens with, and the result the engine calculates for them.

Inputs

Conditioned floor area
2,000 ft²
Capacity entered as
Tons
Cooling capacity
3 tons
Building
House or apartment

Result

Floor area per ton
667 ft²
Cooling capacity per square foot
18 BTU/h·ft²
Cooling capacity per square foot
5.28 W/ft²
Capacity
3 tons

3 tons for 2,000 ft² is 667 ft² per ton (18 BTU/h per ft²).

Assumptions

  • 1 ton = 12,000 BTU/h; 1 BTU/h = 0.29307 W.
  • The home comparison uses the 1,000 ft²/ton threshold and 1,431 ft²/ton average reported for 40 Manual J calculations on the ACCA blog (a guest article, not an ACCA standard).

Limitations

  • Square feet per ton is a benchmark only. Loads depend on climate, insulation, windows, air leakage and occupancy, so two homes of the same size can need very different equipment.
  • For commercial buildings no comparison range is given; use a load calculation.

Frequently asked questions

How many square feet does a 3-ton AC cool?

There is no single answer. At the 1,000–1,500 ft² per ton that Manual J calculations commonly give for homes, 3 tons would suit roughly 3,000–4,500 ft² — but only a load calculation for your house can say.

Is 500 square feet per ton too much cooling?

For most modern homes, probably. It is the old rule of thumb, and published Manual J results for homes are usually above 1,000 ft² per ton. Check with a load calculation.

What does W/ft² mean?

Cooling capacity in watts per square foot of floor — the same density expressed in metric power units, often used for commercial buildings and equipment rooms.

Sources

  1. Manual J Load Calculations vs. Rules of Thumb — ACCA HVAC Blog (A. Bailes). Square feet per ton is not a sizing method; Manual J results commonly exceed 1,000 ft² per ton.
  2. Proper Sizing of HVAC Systems — U.S. DOE Building Science Education Solution Center. Rules of thumb lead to oversized systems; loads should be calculated with Manual J.
  3. NIST Guide to the SI (SP 811), Appendix B.9 — conversion factors — National Institute of Standards and Technology. 1 ton of refrigeration = 12,000 BTU/h; 1 BTU/h = 0.2930711 W; 1 atm = 101.325 kPa.

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