What Tonnage Is My AC Unit? The 60-Second Method
Maybe you're replacing an old unit, comparing quotes from HVAC contractors, or just curious why one room never cools down. Whatever brought you here, you don't need a technician to tell the tonnage of your AC unit. You need about a minute and these four steps:
- Head outside to the condenser.That's the big metal box with the fan on top, humming away next to your house.
- Find the data plate.It's a metal or foil sticker on the side panel, usually near the spot where the copper refrigerant lines run into the cabinet.
- Locate the model number. It's the line marked M/N or Model No. — careful not to grab the serial number (S/N) sitting right next to it.
- Spot the capacity code and divide by 12. Somewhere in that string of letters and digits is an even number divisible by 6: 18, 24, 30, 36, 42, 48, or 60. That's your cooling capacity in thousands of BTUs per hour. Divide by 12 and you've got tons.
That's genuinely all there is to it. A model number with 24 in the right spot is a 2 ton unit, 36 is 3 tons, 48is 4 tons. This works because one ton of cooling equals 12,000 BTU/hr, and manufacturers bake that number straight into their model numbers. The same trick works whether you're trying to determine AC tonnage from a model number on a Carrier, Goodman, Trane, Lennox, Rheem, or York — pretty much every brand sold in the US plays by this rule.
Where to Find the Tonnage on an AC Unit
People often expect to see "3 TONS" written somewhere on the unit. Sorry, but manufacturers are not that generous. The tonnage on an AC unit is almost never spelled out — it lives inside the model number on the data plate (some folks call it the nameplate or rating plate). On the outdoor condenser, that plate sits on the side or back panel, typically close to the electrical disconnect and the refrigerant line connections.
One thing that trips people up: the plate lists both a model number and a serial number, usually stacked right on top of each other. The model number (M/N)is the one that contains the size. The serial number (S/N) encodes when the unit was built, not how big it is. If you've been staring at the serial number wondering where the tonnage went, that's why.
If you have a split system, your indoor air handler or furnace coil has its own data plate too, and its model number also carries a capacity code. But for cooling capacity, the outdoor unit's plate is the one to trust. And if you're checking a window or portable AC, you're off the hook entirely — those print the BTU rating right on the label, so just divide it by 12,000 to get tons.
How to Read the Tonnage Code in a Model Number
So how do you read the tonnage once you're looking at the model number? Manufacturers write capacity in thousands of BTUs per hour, in steps of half a ton (6,000 BTU). That's why the same seven numbers show up across every brand:
| Code in Model Number | AC Tonnage | Cooling Capacity (BTU/hr) |
|---|---|---|
| 18 (or 018) | 1.5 Tons | 18,000 |
| 24 (or 024) | 2 Tons | 24,000 |
| 30 (or 030) | 2.5 Tons | 30,000 |
| 36 (or 036) | 3 Tons | 36,000 |
| 42 (or 042) | 3.5 Tons | 42,000 |
| 48 (or 048) | 4 Tons | 48,000 |
| 60 (or 060) | 5 Tons | 60,000 |
Let's decode two real ones so you can see it in action:
Trane 4TTR6036J1000A — the zero-padded 036after the series letters is the capacity code. 36,000 BTU/hr ÷ 12,000 = a 3 ton unit.
Goodman GSX140361 — GSX is the product line, 14 is the SEER rating, and 036is the capacity. Again, 3 tons. Notice how the 14 could fool you if you didn't know it was the efficiency rating — the capacity code is always one of those seven numbers from the chart.
Watch out for Carrier and Bryant: their model numbers startwith digits like 24, 25, or 38 — that's the product family, not the size. In a Carrier 24ABC636, the 36 near the end is the real capacity code. The 24 up front means nothing about tonnage.
AC Tonnage Codes by Brand: Quick Reference
Every brand hides the code in a slightly different spot. Here's where to look on the major US brands:
| Brand | Where the Code Sits | Example → Decoded |
|---|---|---|
| Carrier & Bryant | Mid-to-late digits (ignore the leading 24/25/38 family code) | 24ABC636 → 3 tons |
| Goodman & Amana | Digits right after the series and SEER rating | GSX140361 → 3 tons |
| Trane & American Standard | Zero-padded 3-digit group after the series | 4TTR6036J1000A → 3 tons |
| Lennox | Dash-separated 3-digit group | ML14XC1-036-230 → 3 tons |
| Rheem & Ruud | Two digits after the series and SEER number | RA1436AJ1NA → 3 tons |
| York | Two digits after the 4-letter prefix | YCJF36S41S1 → 3 tons |
Don't stress about memorizing any of this — the decoder at the top of this page already knows each brand's format. Pick your brand, paste the model number, done.
How to Find AC Tonnage Without a Model Number
Labels fade. A unit that's been baking in the sun for 15 years might have a data plate you can barely read. If the model number is gone, here's how to find your AC tonnage without it, in the order I'd try:
1. Check the RLA on the data plate
Even on faded plates, the electrical ratings often survive because they're stamped for code compliance. Find RLA(Rated Load Amps) for the compressor. As a rough rule of thumb, residential compressors draw about 5 to 7 amps per ton at 240V. So an RLA around 16–19 usually points to a 3 ton unit. It's a ballpark, not gospel — but it narrows things down fast.
2. Use the serial number to ask the manufacturer
Here's the thing about serial numbers: you can't determine AC tonnage from a serial number by reading it yourself, because it encodes the manufacture date and factory, not the size. But the manufacturer can. Call the brand's support line (or use their online lookup if they have one), give them the serial number, and they'll pull up the full spec sheet for your exact unit. Slower than the other methods, but it's the definitive answer.
3. Peek at the breaker size
Open your electrical panel and find the breaker labeled for the AC or condenser. A 20–30 amp breaker usually serves a 1.5 to 3 ton unit, while 35–50 amps suggests 3.5 to 5 tons. Of all three methods this is the fuzziest, since electricians size breakers with margin — treat it as a sanity check, not an answer.
And if the unit is so old or unlabeled that nothing works? Flip the problem around: figure out what size the space actually needs with our AC tonnage calculator. If your mystery unit struggles to keep up with that number, it's probably undersized — and you'll want the right size anyway when it's time to replace it.
Found Your Tonnage? Here's What to Do Next
Knowing your unit is, say, 3 tons is only half the story. The more useful question is whether 3 tons is what your home actually needs. Plenty of houses in the US are running units that were sized by guesswork decades ago. Run your room or home through our AC Unit Tonnage Calculator and compare — if the numbers are far apart, that explains a lot about high bills or rooms that never feel right.
Need the same number in different units? The Ton to BTU converter flips between tons and BTUs instantly. And if you just discovered your unit is old enough to vote, our SEER savings calculator will show you what upgrading to a modern high-efficiency unit would save you per year — the answer is usually more motivating than you'd expect.