Free · Equipment sizing
AC Tonnage Calculator
Enter the square footage and climate to get the air conditioner size in tons and BTUs, with the Manual S sizing window applied. Includes BTU, ton and kilowatt conversions.
The space
Conditioned floor area, not the lot.
Convert BTU to tons
3 tons · 10.55 kW · 10,551 watts
Recommended AC size
3.5tons
Cooling load
40,000
BTU/h
Exact tonnage
3.33
tons before rounding
Sq ft per ton
480
Typical 500–600 here
BTU per sq ft
25
after adjustments
Manual S check
Standard sizes and what they cover in a warm climate
| Size | BTU/h | Sq ft (average build) | kW |
|---|---|---|---|
| 1.5 ton | 18,000 | 667–783 | 5.28 |
| 2 ton | 24,000 | 889–1,043 | 7.03 |
| 2.5 ton | 30,000 | 1,111–1,304 | 8.79 |
| 3 ton | 36,000 | 1,333–1,565 | 10.55 |
| 3.5 ton | 42,000 | 1,556–1,826 | 12.31 |
| 4 ton | 48,000 | 1,778–2,087 | 14.07 |
| 5 ton | 60,000 | 2,222–2,609 | 17.58 |
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How AC tonnage is calculated
A ton of cooling is 12,000 BTU per hour, the heat needed to melt a ton of ice in a day. To size a unit you estimate the house's peak cooling load in BTU/h, divide by 12,000, and round to a standard size the way ACCA Manual S allows: between 95% and 115% of the load.
The base rate is the number that matters most. Hot climates need about 30 BTU per square foot, warm ones 25, the middle of the country 22, and northern states 15–18. Poor insulation adds 15%, good insulation takes off 12%, and heavy west sun adds 10%. This page assumes 8-foot ceilings, double-pane windows and a single story; the full load calculator lets you change all of those and gives you the heating load too.
Bigger is not better
An oversized air conditioner satisfies the thermostat in a few minutes and shuts off before the coil has pulled much moisture out of the air. The house ends up cool and sticky, the equipment cycles itself to death, and the customer calls you back. Right-sized equipment runs longer, quieter cycles and dehumidifies properly. When the load lands between sizes, go down, not up, unless a Manual J says otherwise.
Quick conversions
- 1 ton = 12,000 BTU/h = 3.517 kW of cooling
- 1 kW = 3,412 BTU/h
- 1.5 ton = 18,000 · 2 ton = 24,000 · 2.5 ton = 30,000 · 3 ton = 36,000 · 4 ton = 48,000 · 5 ton = 60,000 BTU/h
- Nominal airflow is 400 CFM per ton; the CFM calculator covers the rest.
Frequently asked questions
What size AC do I need for a 2,000 square foot house?
About 3 tons in a mixed climate, 3.5 to 4 tons in a hot climate like Texas or Florida, and 2.5 tons in the northern states, assuming average insulation. Poor insulation, lots of west-facing glass or vaulted ceilings can push each of those up half a ton.
How many square feet will a 3-ton AC cool?
Roughly 1,200–1,500 square feet in a hot climate, 1,600–2,000 in a mixed climate, and up to 2,400 in a cool climate with good insulation. The table on this page shows the range for the climate you selected.
How do I convert BTU to tons?
Divide BTU per hour by 12,000. A 36,000 BTU unit is 3 tons; a 24,000 BTU unit is 2 tons. Type any BTU figure into the converter above to see tons, kilowatts and watts.
Can I use the model number to find tonnage?
Usually. Most manufacturers put the nominal BTU in the model number in thousands: 24 means 24,000 BTU or 2 tons, 36 means 3 tons, 48 means 4 tons, 60 means 5 tons. Check the data plate to confirm.
Is a half-ton oversize acceptable?
Manual S allows cooling equipment up to 115% of the load, so a half-ton over on a 3-ton load (117%) is just outside the window and a half-ton over on a 4-ton load (112%) is inside it. Heat pumps in cold climates get more latitude because the heating load usually governs.