AC size chart by square footage
Recommended central AC size in tons for a home with 8 ft ceilings, average insulation and average sun. One ton of cooling equals 12,000 BTU per hour.
| Home size | Hot IECC 1–2 | Warm IECC 3 | Mixed IECC 4 | Cold IECC 5 | Very cold IECC 6–7 |
|---|---|---|---|---|---|
| 600 sq ft | 1.5 | 1.5 | 1.5 | 1.5 | 1.5 |
| 800 sq ft | 2 | 1.5 | 1.5 | 1.5 | 1.5 |
| 1,000 sq ft | 2 | 2 | 1.5 | 1.5 | 1.5 |
| 1,200 sq ft | 2.5 | 2.5 | 2 | 2 | 2 |
| 1,500 sq ft | 3.5 | 3 | 2.5 | 2.5 | 2.5 |
| 1,800 sq ft | 4 | 3.5 | 3 | 3 | 3 |
| 2,000 sq ft | 4.5 | 4 | 3.5 | 3 | 3 |
| 2,200 sq ft | 5 | 4 | 4 | 3.5 | 3.5 |
| 2,500 sq ft | 2 systems | 5 | 4.5 | 4 | 4 |
| 3,000 sq ft | 2 systems | 2 systems | 5 | 5 | 4.5 |
Residential central air conditioners top out at 5 tons. Homes that need more are usually split into two systems, often one per floor.
How many BTU per square foot?
A common starting point is 20 BTU per square foot, but the right figure depends on climate. A home in Phoenix needs far more cooling per square foot than the same home in Minneapolis.
| Climate zone | BTU per sq ft | Sq ft per ton | Example cities |
|---|---|---|---|
| Hot · IECC 1–2 | 26.7 | 450 | Miami, Houston, Phoenix |
| Warm · IECC 3 | 22.9 | 525 | Atlanta, Dallas, Los Angeles |
| Mixed · IECC 4 | 20.9 | 575 | Nashville, St. Louis, Baltimore |
| Cold · IECC 5 | 19.2 | 625 | Chicago, Denver, Boston |
| Very cold · IECC 6–7 | 18.5 | 650 | Minneapolis, Burlington, Duluth |
What changes the size you need
- Ceiling height. The chart assumes 8 ft ceilings. A home with 10 ft ceilings has 25% more air to cool.
- Insulation and air leaks. An older, drafty home can need 15% more capacity. A newer home built to modern energy codes can need about 10% less.
- Windows and sun. Large west- and south-facing windows add heat all afternoon. Shade trees and awnings reduce the load.
- Ductwork. Ducts in a hot attic lose cooling before it reaches the rooms. Sealing and insulating them is usually cheaper than buying a bigger unit.
- Occupants and appliances. Each person adds about 600 BTU per hour of heat. Kitchens add more.
Window AC size by room
For a single room, ENERGY STAR publishes a simple chart. Reduce the size by 10% for a heavily shaded room and increase it by 10% for a very sunny one. Add 600 BTU for each person beyond two, and 4,000 BTU for a kitchen.
| Room area | Capacity needed | Example room |
|---|---|---|
| 100–150 sq ft | 5,000 BTU | 10 × 12 ft bedroom |
| 150–250 sq ft | 6,000 BTU | 12 × 15 ft bedroom |
| 250–300 sq ft | 7,000 BTU | 15 × 18 ft living room |
| 300–350 sq ft | 8,000 BTU | 16 × 20 ft family room |
| 350–400 sq ft | 9,000 BTU | 18 × 20 ft room |
| 400–450 sq ft | 10,000 BTU | 20 × 22 ft room |
| 450–550 sq ft | 12,000 BTU | Studio apartment |
| 550–700 sq ft | 14,000 BTU | Open living and dining |
| 700–1,000 sq ft | 18,000 BTU | Small apartment |
| 1,000–1,200 sq ft | 21,000 BTU | Converted garage |
| 1,200–1,400 sq ft | 23,000 BTU | Large open floor |
| 1,400–1,500 sq ft | 24,000 BTU | Large open floor |
Why a bigger AC is not better
An oversized air conditioner reaches the thermostat setting in a few minutes and shuts off. These short cycles cool the air without running long enough to pull moisture out of it, so the house feels cold and damp. Short cycling also wears out the compressor sooner and raises electric bills.
An undersized unit runs continuously on the hottest afternoons and may never reach the set temperature. If your calculated load falls between two sizes, choose the smaller one in humid climates and the larger one in dry, hot climates, or consider a variable-speed system that adjusts its output.
When you need a Manual J
A Manual J load calculation, defined by the Air Conditioning Contractors of America (ACCA), checks every room for wall area, window orientation, insulation level and air leakage. Many building departments require one for a new system. Use this calculator to know what size to expect, and ask your contractor for the Manual J report if their recommendation differs by more than half a ton.
Frequently asked questions
What size AC do I need for a 1,500 sq ft house?
Most 1,500 sq ft homes need a 2.5-ton AC in mixed and cold climates, a 3-ton unit in warm climates, and 3.5 tons in hot climates such as Florida, Texas or Arizona.
What size AC do I need for a 2,000 sq ft house?
A 2,000 sq ft home typically needs 3 to 3.5 tons in mixed and cold climates, 4 tons in warm climates and 4.5 tons in hot climates.
How many square feet does a 3-ton AC cool?
A 3-ton AC (36,000 BTU/h) cools about 1,350 sq ft in a hot climate, 1,575 sq ft in a warm climate, 1,725 sq ft in a mixed climate and up to 1,950 sq ft in a very cold climate.
What size window AC do I need for a 12 × 12 room?
A 12 × 12 ft room is 144 sq ft, so a 5,000 BTU window unit is enough. Choose 6,000 BTU if the room gets strong afternoon sun.
Is it better to oversize an air conditioner?
No. An oversized AC short-cycles, removes less humidity and wears out faster. Choose the size closest to your calculated load.
How many BTU is one ton of air conditioning?
One ton of cooling equals 12,000 BTU per hour, the heat needed to melt one ton of ice in 24 hours.
This calculator gives an estimate for planning. Final equipment size should come from a Manual J load calculation by a licensed HVAC contractor. Climate zones follow the IECC map; room sizes follow the ENERGY STAR room air conditioner guide.