AC Tonnage & Sizing Guide
How to determine what size AC unit you need — and why getting it right matters.
What Is AC Tonnage?
AC tonnage measures cooling capacity, not weight. One ton of cooling equals 12,000 BTU (British Thermal Units) per hour. A 2-ton unit produces 24,000 BTU/hr of cooling, a 3-ton produces 36,000 BTU/hr, and so on.
Residential AC units typically range from 1.5 to 5 tons. The right size depends on your home's square footage, insulation, climate zone, number of windows, and other factors.
Tonnage Reference Table
Use this table to understand the relationship between BTU codes (found in model numbers), tonnage, and the approximate home size each unit can cool:
| BTU Code | Tons | BTU/hr | Sq Ft Range |
|---|---|---|---|
| 009 | 0.75 | 9,000 | 300–375 sq ft |
| 012 | 1 | 12,000 | 400–500 sq ft |
| 018 | 1.5 | 18,000 | 600–750 sq ft |
| 024 | 2 | 24,000 | 800–1,000 sq ft |
| 030 | 2.5 | 30,000 | 1,000–1,250 sq ft |
| 036 | 3 | 36,000 | 1,200–1,500 sq ft |
| 042 | 3.5 | 42,000 | 1,400–1,750 sq ft |
| 048 | 4 | 48,000 | 1,600–2,000 sq ft |
| 060 | 5 | 60,000 | 2,000–2,500 sq ft |
These are general guidelines. Actual requirements vary based on climate, insulation, ceiling height, and sun exposure.
Why Correct Sizing Matters
Installing the wrong size AC unit causes real problems — both oversized and undersized units perform poorly:
Oversized Unit
- Short cycling — turns on/off too frequently
- Poor humidity removal
- Higher energy bills
- Premature wear on the compressor
- Uneven temperatures throughout the home
Undersized Unit
- Runs constantly without reaching set temperature
- Higher energy bills from continuous operation
- Excessive wear and shorter lifespan
- Home never feels comfortable on hot days
- Frozen evaporator coil from overwork
How to Determine Your Current Tonnage
The easiest way is to look at your current unit's model number and find the 3-digit BTU code (see the table above). For example, if your model number is GSX160361, the code 036 means 3 tons.
For a like-for-like replacement, we typically match your current tonnage unless there's a reason to change (e.g., you added square footage to your home). Our free jobsite inspection confirms the correct size.
Manual J Load Calculation
For new construction or major renovations, a Manual J load calculation is the gold standard for sizing. It accounts for square footage, insulation, windows, orientation, local climate data, and more. Ask your contractor if one is needed.
Don't want to decode model numbers? Use our Dataplate Scanner to identify your tonnage automatically.
Ready to Get Started?
Schedule a free site visit — or use our Dataplate Scanner to identify your system first.