How do I find AC tonnage from the model number?

The middle two or three digits of the model number are the nominal capacity in thousands of BTU per hour. Divide by 12 to get tonnage, since one ton equals 12,000 BTU/hr. For example, a model containing 036 is 36,000 BTU/hr, which is 3 tons.

My model number has two matching numbers — which is the size?

Modern models often include the SEER2 rating right before the capacity code. The three-digit code (036, 048, 060) is the capacity and the two-digit number is usually SEER.

How accurate is decoding tonnage from the model number?

The size-code standard is reliable across major North American brands, so a confident match is almost always correct. Always confirm against the rating plate or AHRI Directory before buying parts or a replacement.

AC Tonnage Calculator by Model Number — Decode Any AC or Heat Pump Size

HVAC Field Tools

AC Tonnage Calculator by Model Number

Type the model number off your outdoor unit’s rating plate. This tool decodes the size code and tells you the tonnage and BTU/hr in seconds — no chart hunting.

Model number

Find it on the metal data plate on the side of the outdoor condenser — the line labeled “Model” or “M/N”.

Brand (optional — improves accuracy)

Straight answer

How model numbers show AC tonnage

On almost every residential AC and heat pump, the middle two or three digits of the model number are the nominal capacity in thousands of BTU per hour. Divide that number by 12 to get tonnage, because one ton of cooling equals 12,000 BTU/hr. So a model containing 036 is a 36,000 BTU/hr unit, which is 3 tons. A model with 048 is 48,000 BTU/hr, or 4 tons.

The number is almost always one of a fixed set of sizes, which is why the decoder above can find it even when the rest of the model number is a jumble of series letters, SEER ratings, and voltage codes.

AC size code reference chart

Code	BTU/hr	Tonnage	Typical area cooled*
018	18,000	1.5 tons	600–900 sq ft
024	24,000	2 tons	900–1,200 sq ft
030	30,000	2.5 tons	1,200–1,500 sq ft
036	36,000	3 tons	1,500–1,800 sq ft
042	42,000	3.5 tons	1,800–2,100 sq ft
048	48,000	4 tons	2,100–2,400 sq ft
060	60,000	5 tons	2,400–3,000 sq ft

*Rough rule of thumb only. Real sizing depends on climate, insulation, windows, and ceiling height — a proper Manual J load calculation can land a full ton different from the square-footage guess.

Worked example

Decoding a real model number

Say your Trane condenser reads 4TTR4036L1000AA. Here’s how to read it:

Ignore the front — 4TTR4 is Trane’s series and product family, not the size.
Find the capacity block: 036. That’s the number from the size chart.
036 means 36,000 BTU/hr. Divide by 12,000 → 3 tons.
The trailing L1000AA is voltage, refrigerant, and revision info — not size.

Same logic works on a Goodman GSXC180601: the 18 is the SEER2 rating and 060 is the capacity — a 5-ton unit. This is exactly the trap the decoder handles by prioritizing the three-digit capacity code over stray two-digit numbers.

By brand

Where each brand hides the size code

The capacity code is standardized, but its position in the model number shifts between manufacturers. Quick map:

Brand	Example	Size code
Carrier / Bryant	24ACC636A003	36 → 3 tons
Trane / Am. Standard	4TTR4036L	036 → 3 tons
Goodman / Amana	GSXC180601	060 → 5 tons
Lennox	XC16-036-230	036 → 3 tons
Rheem / Ruud	RA1648AJ1NA	48 → 4 tons
York / Coleman	YCG36B21S	36 → 3 tons

FAQ

Common questions

What if my model number has no matching size code?

A few older or light-commercial units use non-standard numbering, and some mini-splits list capacity as 9, 12, or 24 (thousand BTU). If the decoder can’t find a match, read the rating plate directly — capacity is often printed in a separate “BTU/hr” or “Cooling Capacity” field, or look up the model on the AHRI Directory for the certified rating.

Is tonnage the same as how much area it cools?

Not exactly. Tonnage is the unit’s cooling capacity, but the area it can actually keep comfortable depends on your climate, insulation, sun exposure, and ceiling height. The square-footage figures here are a starting rule of thumb, not a sizing recommendation.

Does the decoder work for heat pumps too?

Yes. Heat pumps use the same capacity numbering as straight AC condensers, so the same code (018–060) maps to the same tonnage. The size code describes cooling capacity in both cases.

My model number has two numbers that match — which is the size?

Modern models often include the SEER2 efficiency rating (like 14, 15, 16, 18) right before the capacity code. When two candidates appear, the three-digit code (036, 048, 060) is the capacity and the two-digit one is usually SEER. The decoder above prioritizes the three-digit capacity code for this reason and lists any other numbers it found so you can cross-check.

How accurate is this?

The size-code standard is reliable across the major North American brands, so a confident match is almost always correct. Because model formats vary, always confirm against the rating plate or the AHRI Directory before buying parts or a replacement — the decoder is a fast lookup, not a substitute for the nameplate.

Good to know: This tool reads the nominal capacity encoded in the model number. Actual delivered capacity can differ with the matched coil and air handler. For replacements, parts, or warranty work, always verify against the unit’s rating plate and the AHRI Directory. This is an informational tool, not professional sizing advice.