BTUFit › Central AC size
Central AC size calculator
Most homes need 1.5 to 5 tons of central air (one ton is 12,000 BTU/h), in half-ton steps. A 3-ton unit covers about 1,600 to 2,400 sq ft, but climate and insulation move that as much as floor area does: the hot, humid South runs ~24 BTU/sq ft, a cold climate ~15.
Typical replacement cost (US ballpark, 2026): a whole-house central AC change-out often lands around $4,000–$12,000+ installed, depending on tonnage, SEER2, and whether ducts need work. Public cost guides (Angi, HomeGuide and similar) commonly put a standard 3-ton replacement in the $5,000–$9,000 band when existing ducts are usable. New duct runs, panel upgrades, and heat-pump conversions run higher. These are labeled national estimates, not a bid for your ZIP.
Tonnage by house size and climate
Average insulation, whole-house cooling, every 200 sq ft from 1,000 to 3,000. Drafty or newly-tight envelopes move each row about half a ton in the obvious direction; the calculator above does that part. The two footprints with their own page carry an installed-cost band and the duct-condition detail.
| House | Hot-humid | Hot-dry | Mixed | Cool | Cold |
|---|---|---|---|---|---|
| 1,000 sq ft | 2 tons | 2 tons | 1.5 tons | 1.5 tons | 1.5 tons |
| 1,200 sq ft | 2.5 tons | 2 tons | 2 tons | 1.5 tons | 1.5 tons |
| 1,400 sq ft | 3 tons | 2.5 tons | 2.5 tons | 2 tons | 2 tons |
| 1,500 sq ft | 3 tons | 3 tons | 2.5 tons | 2 tons | 2 tons |
| 1,600 sq ft | 3 tons | 3 tons | 2.5 tons | 2.5 tons | 2 tons |
| 1,800 sq ft | 3.5 tons | 3.5 tons | 3 tons | 2.5 tons | 2.5 tons |
| 2,000 sq ft | 4 tons | 3.5 tons | 3.5 tons | 3 tons | 2.5 tons |
| 2,200 sq ft | 4.5 tons | 4 tons | 3.5 tons | 3 tons | 3 tons |
| 2,400 sq ft | 5 tons | 4.5 tons | 4 tons | 3.5 tons | 3 tons |
| 2,600 sq ft | 5 tons | 5 tons | 4.5 tons | 3.5 tons | 3.5 tons |
| 2,800 sq ft | 5.5 tons | 5 tons | 4.5 tons | 4 tons | 3.5 tons |
| 3,000 sq ft | 6 tons | 5.5 tons | 5 tons | 4.5 tons | 4 tons |
How the estimate works
The calculator applies a climate-tuned load factor (from about 15 BTU/sq ft in cold climates to 24 BTU/sq ft in the hot, humid South), then adjusts ±10–15% for the envelope: older drafty houses carry more load, tight new builds less. The result rounds to the nearest half ton.
Treat it as a budgeting number and a BS-detector for quotes. The real sizing method is a Manual J calculation, which any installer quoting you thousands of dollars should be willing to run. If a contractor sizes your system by square footage alone from the driveway, get another quote.
Frequently asked questions
How many square feet does a 3-ton AC unit cover?
Roughly 1,600–2,400 sq ft depending on climate and insulation. In a hot, humid climate a 3-ton (36,000 BTU) unit covers about 1,500–1,700 sq ft; in a cool northern climate the same unit stretches past 2,300 sq ft. That spread is why square footage alone can't pick your size.
What size AC unit do I need for a 2,000 sq ft house?
From about 3 tons in a cool climate with good insulation to 4 tons in the hot, humid South with an older envelope. The 2,000 sq ft page has the full breakdown.
How much does it cost to replace a central AC unit?
A whole-house central AC change-out often lands around $4,000–$12,000+ installed, depending on tonnage, SEER2 and duct condition; a standard 3-ton replacement commonly runs $5,000–$9,000 when the existing ducts are usable. New duct runs, panel upgrades and heat-pump conversions run higher. Labeled 2026 US ranges, not a bid for your ZIP.
Should I just replace my old unit with the same size?
Not blindly. Many older systems were oversized on installation, and if you've since added attic insulation or new windows, the correct size may have dropped. A like-for-like swap repeats a 20-year-old guess. Ask the installer for a Manual J load calculation; a good one does it as a matter of course.
What if my house needs more than 5 tons?
Residential equipment tops out at 5 tons. Bigger loads are handled with two systems (commonly one per floor, which also gives you zoning) rather than one huge unit. Two 3-ton systems almost always outperform one 6-ton on comfort.
Is this a Manual J calculation?
No. Manual J models your actual walls, windows, orientation, infiltration and duct losses, room by room. This is the honest rule of thumb (BTU per square foot tuned by climate zone and insulation), good for budgeting and for sanity-checking a contractor's quote, not for final equipment selection.