AC Tonnage Calculator
Size a central air conditioner for your home. Enter the square footage, ceiling height and occupants, then pick your climate, sun exposure and insulation — and get the cooling load in BTU/hr and the recommended system size in tons, rounded up to a standard size. Includes a full load breakdown, by-square-footage and by-climate tables, and a downloadable PDF.
| Area | BTU / hr | Calc tons | Size |
|---|---|---|---|
| Enter a space to compare | |||
| Climate | BTU / ft² | BTU / hr | Size |
|---|---|---|---|
| Enter a space to compare | |||
How to use the AC tonnage calculator
Four quick steps turn your home’s size and conditions into a cooling load in BTU per hour and a recommended central AC size in tons — with by-area and by-climate tables and a downloadable report.
Enter the space
Give the square footage you’re cooling, the ceiling height, and how many people regularly use it.
Pick your climate
Choose hot, warm, moderate or cool — this sets the base BTU per square foot.
Set sun, insulation & kitchen
Adjust for shade or strong sun, insulation quality, and whether the area includes a kitchen.
Read results & save a PDF
Get BTU/hr and recommended tons, compare areas and climates — then download a report.
How the AC size is calculated
A climate-based BTU per square foot, adjusted for sun, insulation and ceiling height, plus extra loads for people and a kitchen — then converted to tons and rounded up to a standard size. Here is the exact math the calculator runs.
Worked example — 1,500 sq ft home, 8 ft ceilings, 2 occupants, moderate climate, average sun and insulation, no kitchen
Adjusted rate: 22 × 1.0 × 1.0 = 22 BTU/ft² · Ceiling factor: 8 ÷ 8 = 1.0
Base load: 1,500 × 22 × 1.0 = 33,000 BTU/hr · Extra loads: 0
Calculated: 33,000 ÷ 12,000 = 2.75 tons · Recommended: round up → 3 tons
≈ 33,000 BTU/hr → a 3-ton central AC (about 545 sq ft per ton).
AC sizing reference charts
Handy lookups for climate rates, typical sizes by square footage, and the adjustments the calculator applies. Always confirm the final size with a Manual J.
| Climate | BTU / sq ft | Sq ft per ton | Typical regions |
|---|---|---|---|
| Hot | 28 | ~430 | Gulf Coast, desert Southwest, South Florida |
| Warm | 24 | ~500 | Southeast, southern Plains |
| Moderate | 22 | ~545 | Mid-Atlantic, central US |
| Cool | 20 | ~600 | Northern states, Pacific Northwest |
Sq ft per ton = 12,000 ÷ BTU per sq ft, before sun, insulation and ceiling adjustments.
| Area | BTU / hr | Calculated tons | Recommended |
|---|---|---|---|
| 500 sq ft | 11,000 | 0.92 | 1.5 ton |
| 1,000 sq ft | 22,000 | 1.83 | 2 ton |
| 1,500 sq ft | 33,000 | 2.75 | 3 ton |
| 2,000 sq ft | 44,000 | 3.67 | 4 ton |
| 2,500 sq ft | 55,000 | 4.58 | 5 ton |
Average sun and insulation, 8 ft ceilings, 2 occupants, no kitchen. Loads above 5 tons are usually split into two systems.
| Factor | Adjustment |
|---|---|
| Sun exposure | Shaded −10% · Average 0% · Sunny +10% |
| Insulation | Good −10% · Average 0% · Poor +15% |
| Ceiling height | Load × (height ÷ 8 ft) |
| Occupants | +600 BTU/hr per person beyond two |
| Kitchen | +4,000 BTU/hr |
Rule-of-thumb factors. A Manual J also accounts for windows, orientation, duct losses and local design temperatures.
Everything the calculator works out
Square footage and a few conditions give you the full sizing picture — cooling load, calculated and recommended tons, and side-by-side comparisons.
Key figures behind the estimate
Built for anyone sizing central air
From replacing an old unit to pricing a new install, the same calculator turns a home’s size into a sensible starting tonnage.
Getting quotes for a new system and wants to know whether the size contractors suggest makes sense.
- Enter your square footage
- Pick your climate
- Compare to your quotes
Touring a home and wants to know if the existing AC is undersized or oversized for the space.
- Use the listing’s square footage
- Check the unit’s tonnage
- Flag a mismatch early
Finishing a basement or adding a room and needs to know if the current system can handle the extra load.
- Add the new square footage
- Factor in tall ceilings
- See if you jump a size
7 things to know about AC sizing
A few details keep an AC estimate realistic and the house comfortable for years.
AC tonnage calculator FAQ
The sizing, tonnage and load questions people ask most about central air conditioning.
Multiply your square footage by a base cooling rate for your climate, adjust for sun, insulation, ceiling height, occupants and a kitchen, then divide by 12,000 to get tons. Round up to the next standard size.
As a rough guide, a home in a moderate climate needs about 22 BTU per square foot, so a 1,500-square-foot house needs about 33,000 BTU per hour, or 2.75 tons, which rounds up to a 3-ton system. Hot climates need more, around 28 BTU per square foot, and cool climates less, around 20.
Treat this as a planning number only. The size you actually install should come from a Manual J load calculation done by a licensed HVAC contractor.
One ton of cooling equals 12,000 BTU per hour, so the area it covers depends on how many BTU each square foot needs.
In a moderate climate at about 22 BTU per square foot, one ton cools roughly 545 square feet. In a hot climate at 28 BTU per square foot it covers about 430 square feet, and in a cool climate at 20 BTU per square foot about 600 square feet.
Sunny exposure, poor insulation and tall ceilings shrink that area, while shade and good insulation stretch it. That is why a flat rule like 500 square feet per ton is only a starting point.
Tonnage measures cooling capacity, not weight. One ton of air conditioning removes 12,000 BTU of heat per hour, which is the heat needed to melt one ton of ice over 24 hours, the old way cooling was measured.
A 3-ton air conditioner therefore removes about 36,000 BTU per hour. Central systems for homes are sold in half-ton steps, typically 1.5, 2, 2.5, 3, 3.5, 4 and 5 tons.
Loads above 5 tons are usually handled with two separate systems or zones rather than one larger unit.
Yes. An oversized air conditioner cools the air so quickly that it shuts off before it has run long enough to pull moisture out, a problem called short-cycling. The house can reach the thermostat setting while still feeling damp and clammy.
Frequent starts and stops also wear out the compressor sooner, waste energy, cause uneven temperatures between rooms, and cost more up front for a larger unit.
A correctly sized system runs longer, steadier cycles, so it controls humidity better and is more comfortable. That is why this calculator rounds up only to the next standard size, not beyond it.
Manual J is the industry-standard method from the Air Conditioning Contractors of America (ACCA) for working out how much heating and cooling a specific home needs.
Instead of a square-foot rule, it accounts for window size and orientation, wall and attic insulation, air leakage, duct location, the number of occupants, appliances and your local design temperatures. Many building codes and utility rebate programs require a Manual J before a new system is installed.
Use this calculator to get a ballpark figure, then ask your HVAC contractor for a Manual J to confirm the exact size.
Climate sets the base cooling rate, so it has the biggest effect on the result. This calculator uses about 28 BTU per square foot for hot climates such as the Gulf Coast, the desert Southwest and South Florida, 24 for warm climates, 22 for moderate climates and 20 for cool northern climates.
For a 1,500-square-foot home with average sun and insulation, that works out to about 3.5 tons in a hot climate, 3 tons in a warm or moderate climate, and 2.5 tons in a cool one.
Humid regions also benefit from a system that runs long enough to remove moisture, another reason not to oversize.
Yes. Taller ceilings mean more air to cool, so the calculator scales the load by ceiling height divided by 8 feet. A 10-foot ceiling adds about 25 percent compared with a standard 8-foot ceiling.
People give off heat too: the first two occupants are covered by the base rate, and each additional person adds about 600 BTU per hour. A kitchen adds about 4,000 BTU per hour for the oven, cooktop and refrigerator.
Sun exposure changes the load by about 10 percent either way, and poor insulation adds about 15 percent.
In a moderate climate with average sun and insulation, a 2,000-square-foot home needs about 44,000 BTU per hour, or roughly 3.7 tons, which rounds up to a 4-ton system.
In a warm climate it is also about 4 tons, in a hot climate about 4.7 tons, which rounds up to 5 tons, and in a cool climate about 3.3 tons, which rounds up to 3.5 tons. Tall ceilings, a sunny exposure, poor insulation or extra occupants can push it up a size.
Enter your own details in the calculator for a closer figure, and confirm the final size with a Manual J load calculation.
Estimate only — not a substitute for a Manual J. This calculator sizes a central air conditioner in US units with a square-foot rule of thumb: a base rate of 28, 24, 22 or 20 BTU per square foot by climate, adjusted about ±10% for sun exposure, −10% or +15% for insulation, by ceiling height ÷ 8 ft, plus 600 BTU/hr per occupant beyond two and 4,000 BTU/hr for a kitchen. The load is divided by 12,000 BTU per ton and rounded up to the next standard size from 1.5 to 5 tons. Real cooling loads depend on windows, orientation, air leakage, ductwork and local design temperatures. Have a licensed HVAC contractor perform an ACCA Manual J load calculation before you buy or install a system — oversizing causes short-cycling, poor humidity control and higher bills. For planning purposes only.