How this AC size calculator works
The calculator uses the industry rule of thumb of roughly 18–26 BTU of cooling per square foot, adjusted for your climate zone, and then corrects that base load for insulation quality, sun exposure, ceiling height and household size. It also includes a standard 4,000 BTU kitchen allowance, the same adjustment ENERGY STAR recommends for rooms where heat-producing appliances run.
The result is your estimated cooling load in BTU/hr, the same number converted to tons (1 ton = 12,000 BTU/hr), and the nearest standard equipment size you can actually buy — residential central ACs come in half-ton steps from 1.5 to 5 tons.
AC size chart by square footage
| Home size | Hot climate (Zone 1–2) | Mixed (Zone 3–4) | Cool (Zone 5+) |
|---|---|---|---|
| 1,000 sq ft | 2 tons | 1.5–2 tons | 1.5 tons |
| 1,500 sq ft | 3 tons | 2.5 tons | 2–2.5 tons |
| 2,000 sq ft | 4 tons | 3–3.5 tons | 3 tons |
| 2,500 sq ft | 5 tons | 4 tons | 3.5 tons |
| 3,000 sq ft | 5 tons+ (or 2 systems) | 4.5–5 tons | 4 tons |
Why oversizing an air conditioner backfires
Bigger is not safer with AC. An oversized unit cools the air quickly but shuts off before it has run long enough to remove humidity, leaving the house cold and clammy and cycling on and off constantly. Short cycling wears out the compressor, raises electric bills, and creates uneven temperatures between rooms. Undersizing by a small margin is generally less harmful than oversizing by a full ton — but the right answer is a correctly sized unit.
When to size up half a ton
- Large west-facing window walls with no shading
- Open floor plans with vaulted ceilings
- Homes with hot upstairs rooms and a single system
- Frequent cooking or 6+ occupants
When to size down
- Recently air-sealed and re-insulated homes
- Deep shade from trees or covered porches on the sun side
- Basements included in the square footage (they need far less cooling)
Frequently asked questions
What size AC do I need for a 2,000 sq ft house?
In a hot climate (Texas, Florida, the Desert Southwest) a 2,000 sq ft home typically needs a 4-ton (48,000 BTU) system. In mixed climates 3 to 3.5 tons is usual, and in northern states 3 tons is often enough. Insulation quality and sun exposure can shift the answer by half a ton in either direction.
How many square feet does a 3-ton AC unit cool?
A 3-ton (36,000 BTU) air conditioner typically cools around 1,400–1,600 sq ft in hot climates and 1,800–2,100 sq ft in cooler northern climates, assuming average insulation and 8-ft ceilings.
Is it better to oversize or undersize an air conditioner?
Neither is ideal, but oversizing is usually the more expensive mistake. An oversized AC short-cycles, dehumidifies poorly and wears out faster. If you are between two sizes, most pros pick the smaller one if the ductwork and insulation are in decent shape.
What is a ton of cooling?
One ton of cooling equals 12,000 BTU per hour — historically the heat needed to melt one ton of ice in 24 hours. Residential central ACs range from 1.5 tons (18,000 BTU) to 5 tons (60,000 BTU).
Is this calculator a replacement for a Manual J load calculation?
No. This tool gives a solid planning estimate using industry rules of thumb. Before you buy equipment, a licensed HVAC contractor should perform an ACCA Manual J calculation, which accounts for your exact windows, orientation, infiltration and duct losses.