What Size Is My AC Unit?
Almost every air conditioner and heat pump hides its size in the model number as a capacity code like 036 or 48. Enter your outdoor unit's model and we'll find the code and convert it to tons.
Part of the model number tools. To find the age instead, use the HVAC age lookup.
Model number size lookup
The quick method
- Go to the outdoor unit and find the rating plate (usually on a side panel near the electrical connections).
- Read the line marked Model or M/N.
- Look for one of these numbers inside it: 18, 24, 30, 36, 42, 48 or 60, often with a leading zero.
- Divide by 12. That’s the size in tons.
| Code | Cooling | Size |
|---|---|---|
| 018 / 18 | 18,000 BTU/h | 1.5 tons |
| 024 / 24 | 24,000 BTU/h | 2 tons |
| 030 / 30 | 30,000 BTU/h | 2.5 tons |
| 036 / 36 | 36,000 BTU/h | 3 tons |
| 042 / 42 | 42,000 BTU/h | 3.5 tons |
| 048 / 48 | 48,000 BTU/h | 4 tons |
| 060 / 60 | 60,000 BTU/h | 5 tons |
Where the code sits, brand by brand
| Brand | Example model | Size code |
|---|---|---|
| Carrier | 24ACC636A003 | 36 (after the series digit 6) |
| Bryant | 113ANA036 | 036 |
| Trane / American Standard | 4TTR4036L1000A | 036 |
| Goodman / Amana | GSX140361 | 036 |
| Lennox | XC21-048-230 | 048 |
| Rheem / Ruud | RA1436AJ1NA | 36 (after the SEER, 14) |
| Daikin | DX16SA0361 | 036 |
If you know the brand, our Carrier, Trane and Goodman tools read the exact layout, including furnace input.
Things that trip people up
- Leading numbers that aren’t the size. Carrier’s
24and25, and Trane’s leading2or4, are product codes, not 2 or 4 tons. The tool ignores a number at the very start of the model for this reason. - SEER numbers next to the size. In
GSX140361the14is the efficiency rating; inRA1436the14is SEER and36is the size. - Indoor equipment. Air handlers and coils often carry a range (for example “2.5–3 tons”) or their own codes. Use the outdoor unit for the system size.
- Mini-splits and window units. These usually show capacity directly in BTU (for example 12,000 or 12K) rather than as a code.
- Heat pumps. The same codes apply; the number is the cooling capacity. Heating capacity varies with outdoor temperature and is listed in the product data.
Bigger isn’t better
It’s tempting to replace an AC with a bigger one. An oversized system cools the air quickly and shuts off before it has removed much humidity, so rooms feel cold and clammy. The constant starting and stopping also wears the compressor and wastes energy. Many older homes have systems that were oversized from the start, so when you replace, ask the contractor for a Manual J load calculation instead of matching the old size automatically.
Square-footage rules of thumb (one ton per 400 to 600 square feet) are only a rough sanity check. A well-insulated house in a mild climate can need half the capacity of a leaky one of the same size in Phoenix.
Frequently asked questions
How do I tell what size my AC unit is?
Read the model number on the outdoor unit's rating plate and look for an even number between 18 and 60 that's divisible by 6, often written with a leading zero (018, 024, 030, 036, 042, 048, 060). Divide it by 12 to get tons.
How many BTU is a 3-ton AC?
36,000 BTU per hour. One ton of cooling equals 12,000 BTU/h, the heat needed to melt one ton of ice in 24 hours.
What size AC do I need for my house?
It depends on climate, insulation, windows, layout and air leakage, not just square footage. Rules of thumb like 500 square feet per ton can be badly wrong. A Manual J load calculation is the reliable way to size a new system.
Why does my indoor unit show a different size?
Indoor coils and air handlers are often rated for a range, or slightly larger than the outdoor unit, to get the airflow right. The outdoor unit sets the system's cooling capacity.
Can the model number show the age of my AC?
No. The model is the product and size; the serial number holds the manufacture date. Use our HVAC age lookup for the age.