Sqft to Tons & BTU Calculator
Enter your square footage to get a rough BTU requirement and the equivalent tonnage. Adjust the BTU rate for your climate.
As a rule of thumb, an air conditioner needs about 20 BTU per square foot, and 12,000 BTU equals one ton of cooling. A 1,500 sq ft home needs roughly 1,500 × 20 = 30,000 BTU, which is 30,000 ÷ 12,000 = 2.5 tons.
This is a sizing estimate only. A licensed HVAC contractor should run a Manual J load calculation before you buy — it accounts for insulation, windows, orientation and air sealing.
The 20 BTU per square foot rule
The standard rough estimate for cooling is 20 BTU per square foot of living space. It is a starting point, not a specification.
Adjust the rate for conditions:
- 18 BTU/sq ft — cool northern climates, well-insulated, shaded
- 20 BTU/sq ft — average conditions
- 22–25 BTU/sq ft — hot southern climates, poor insulation, lots of west-facing glass
Add roughly 4,000 BTU if the space includes a kitchen, and about 600 BTU per person if more than two people regularly occupy it.
What a "ton" actually means
A ton of cooling has nothing to do with the weight of the unit. It dates from the era of ice: one ton is the cooling produced by melting one ton of ice over 24 hours, which works out to 12,000 BTU per hour.
Residential systems come in half-ton increments — 1.5, 2, 2.5, 3 tons and up. Always round to the nearest available size rather than the exact calculation.
Why bigger is not better
An oversized air conditioner is a genuine problem, not a safety margin. It cools the air to the thermostat setpoint quickly and shuts off — a pattern called short cycling.
Because it never runs long enough to pull moisture out of the air, the house ends up cold and clammy. Short cycling also wears out the compressor faster and uses more electricity than a correctly sized unit running longer, steadier cycles.
This is exactly why a contractor should run a Manual J calculation. Square footage alone ignores insulation, window area, ceiling height, air sealing and orientation, all of which materially change the answer.
AC size by square footage
Based on 20 BTU per square foot, average conditions.
| Area | BTU needed | Tons | Typical unit |
|---|---|---|---|
| 600 sq ft | 12,000 BTU | 1.0 | 1 ton |
| 900 sq ft | 18,000 BTU | 1.5 | 1.5 ton |
| 1,200 sq ft | 24,000 BTU | 2.0 | 2 ton |
| 1,500 sq ft | 30,000 BTU | 2.5 | 2.5 ton |
| 1,800 sq ft | 36,000 BTU | 3.0 | 3 ton |
| 2,100 sq ft | 42,000 BTU | 3.5 | 3.5 ton |
| 2,400 sq ft | 48,000 BTU | 4.0 | 4 ton |
| 3,000 sq ft | 60,000 BTU | 5.0 | 5 ton |
Frequently asked questions
How many tons of AC do I need per square foot?
A common rule is one ton of cooling per 500 to 600 square feet, which is the same as 20 BTU per square foot. A 1,500 square foot home typically needs about 2.5 tons.
How many BTU per square foot for air conditioning?
About 20 BTU per square foot in average conditions. Use 18 in cool, well-insulated homes and up to 25 in hot climates or poorly insulated buildings.
What size AC do I need for 2,000 sq ft?
Roughly 40,000 BTU, which is about 3.5 tons. Confirm with a Manual J load calculation, since insulation and window area can shift this significantly.
Is a bigger air conditioner better?
No. An oversized unit cools quickly then shuts off, never running long enough to remove humidity. The result is a cold, clammy house, higher energy use and faster compressor wear.
Does square footage alone determine AC size?
It gives a starting estimate only. Ceiling height, insulation quality, window area and orientation, air sealing and local climate all affect the real load, which is what a Manual J calculation measures.