Air Conditioner Size Chart by Square Feet and Climate Zone
Fifteen floor areas against all seven climate zones, in the half ton steps equipment is actually sold in.
Air conditioning is sold in tons, and a ton is 12,000 BTU per hour of cooling. Equipment comes in half ton steps up to five tons and whole tons above that, so the useful answer to how big a system a house needs is not a BTU figure, it is which box on the price list.
The table below is a square foot rule of thumb with a climate adjustment, the same one contractors use to sanity check a quote. It is not a Manual J load calculation and it cannot be. A real load calculation counts your windows, which way they face, how much insulation is in the attic, how leaky the envelope is and how many people live there, and two identical looking houses on the same street can land a full ton apart on those inputs alone.
Use this to know whether a quote is in the right neighborhood. If a contractor proposes something two sizes away from this table, that is the moment to ask for their load calculation.
Cooling size in tons, by floor area and climate zone
| Floor area | Zone 1 | Zone 2 | Zone 3 | Zone 4 | Zone 5 | Zone 6 | Zone 7 |
|---|---|---|---|---|---|---|---|
| 600 sq ft | 1.5 | 1.5 | 1.5 | 1.5 | 1.5 | 1.5 | 1.5 |
| 800 sq ft | 2 | 2 | 2 | 1.5 | 1.5 | 1.5 | 1.5 |
| 1,000 sq ft | 2.5 | 2 | 2 | 2 | 2 | 2 | 2 |
| 1,200 sq ft | 2.5 | 2.5 | 2.5 | 2.5 | 2.5 | 2 | 2 |
| 1,400 sq ft | 3 | 3 | 3 | 2.5 | 2.5 | 2.5 | 2.5 |
| 1,600 sq ft | 3.5 | 3.5 | 3 | 3 | 3 | 3 | 3 |
| 1,800 sq ft | 4 | 3.5 | 3.5 | 3.5 | 3 | 3 | 3 |
| 2,000 sq ft | 4 | 4 | 4 | 3.5 | 3.5 | 3.5 | 3.5 |
| 2,200 sq ft | 4.5 | 4.5 | 4 | 4 | 4 | 4 | 3.5 |
| 2,400 sq ft | 5 | 5 | 4.5 | 4.5 | 4 | 4 | 4 |
| 2,600 sq ft | 5.5 | 5 | 5 | 4.5 | 4.5 | 4.5 | 4.5 |
| 2,800 sq ft | 6 | 5.5 | 5.5 | 5 | 5 | 4.5 | 4.5 |
| 3,000 sq ft | 6 | 6 | 5.5 | 5.5 | 5 | 5 | 5 |
| 3,500 sq ft | 7 | 7 | 6.5 | 6 | 6 | 6 | 5.5 |
| 4,000 sq ft | 8 | 7.5 | 7.5 | 7 | 6.5 | 6.5 | 6.5 |
The full sizing picture for zone 4
| Floor area | Cooling load, BTU/hr | Tons | Size to buy | Heating output, BTU/hr | Furnace input at 80% AFUE | Furnace input at 95% AFUE |
|---|---|---|---|---|---|---|
| 600 sq ft | 16,600 | 1.38 | 1.5 | 27,000 | 33,750 | 28,421 |
| 800 sq ft | 20,600 | 1.72 | 1.5 | 36,000 | 45,000 | 37,895 |
| 1,000 sq ft | 24,600 | 2.05 | 2 | 45,000 | 56,250 | 47,368 |
| 1,200 sq ft | 28,600 | 2.38 | 2.5 | 54,000 | 67,500 | 56,842 |
| 1,400 sq ft | 32,600 | 2.72 | 2.5 | 63,000 | 78,750 | 66,316 |
| 1,600 sq ft | 36,600 | 3.05 | 3 | 72,000 | 90,000 | 75,789 |
| 1,800 sq ft | 40,600 | 3.38 | 3.5 | 81,000 | 101,250 | 85,263 |
| 2,000 sq ft | 44,600 | 3.72 | 3.5 | 90,000 | 112,500 | 94,737 |
| 2,200 sq ft | 48,600 | 4.05 | 4 | 99,000 | 123,750 | 104,211 |
| 2,400 sq ft | 52,600 | 4.38 | 4.5 | 108,000 | 135,000 | 113,684 |
| 2,600 sq ft | 56,600 | 4.72 | 4.5 | 117,000 | 146,250 | 123,158 |
| 2,800 sq ft | 60,600 | 5.05 | 5 | 126,000 | 157,500 | 132,632 |
| 3,000 sq ft | 64,600 | 5.38 | 5.5 | 135,000 | 168,750 | 142,105 |
| 3,500 sq ft | 74,600 | 6.22 | 6 | 157,500 | 196,875 | 165,789 |
| 4,000 sq ft | 84,600 | 7.05 | 7 | 180,000 | 225,000 | 189,474 |
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The btu and ac size calculator takes your own measurements and returns the number for your job, plus the material list as a printable document. Every cell in the table above came out of that same calculator, run at build time.
Bigger is not safer
An oversized air conditioner cools the air to the thermostat setting quickly and then shuts off, which sounds like exactly what you want and is not. Dehumidification happens while the coil runs, and a system that satisfies the thermostat in eight minutes has not run long enough to pull the moisture out. The house ends up cold and clammy.
Short cycling also wears the compressor, because starting is the hardest thing it does. Two sizes too big costs more to buy, costs more to run and dies sooner than the right size would have.
What actually moves a house off this table
Ceiling height is the first one. The table assumes eight feet, and a great room at eighteen is carrying more than twice the air volume of the square footage it reads as. Glass is the second: a wall of west facing windows can add most of a ton on its own in the late afternoon, which is exactly when the system is already working hardest.
Insulation and air sealing move it the other way. A tight house with a properly insulated attic can sit a half ton below this table and hold temperature better than the neighbor at the table figure. That is why a load calculation beats a chart, and why the chart is still worth having when nobody has done one.
Heating is sized separately, and usually larger
The last three columns are the heating side, and they are a different calculation from the cooling side. In zone 4 the heating number comes out well above the cooling number, which is why a furnace and an air conditioner sharing one set of ducts are rarely the same nominal size.
If the heat is a heat pump rather than a furnace, the two get coupled again and the sizing conversation changes: the unit is normally sized to the cooling load, with electric strip heat or a backup fuel covering the coldest hours. In zones 5 and above that backup is doing real work and its capacity belongs in the design, not in a footnote.
Ask for the load calculation
Any contractor quoting a system should be able to hand you a Manual J printout, and most states now require one for a permit on new construction. It takes an hour of somebody's time and it is the difference between a designed system and a guessed one.
If the answer is that they size by square footage, that is what this chart does, and you have just done it yourself for free.
Questions people ask
What size AC unit do I need for a 2,000 square foot house?
Three and a half tons in zones 4 through 7, four tons in zones 1 through 3, at eight foot ceilings and average sun. Tall ceilings, heavy west glass or a poorly insulated attic push it up, and a tight modern envelope pulls it down.
How many square feet does a 3 ton AC cool?
Roughly 1,400 to 1,800 square feet depending on climate zone, which is the range where the three ton column sits in the table above. It is a range rather than a number because the envelope matters as much as the floor area does.
Is it better to oversize or undersize an air conditioner?
Neither, and oversizing is the more common mistake. An oversized unit short cycles, leaves the house humid and wears the compressor out. An undersized one runs continuously on the hottest days and never quite catches up. Size it to the load.
How many BTU is a ton of cooling?
Twelve thousand BTU per hour. A three ton system is 36,000 BTU per hour, a five ton is 60,000. Window units are sold in BTU rather than tons, which is why a 12,000 BTU window unit is a one ton machine.