What Size AC Do I Need?
Most homes need between 1.5 and 5 tons of cooling, and the right size depends on square footage, climate, insulation, ceiling height, and sun exposure - not square footage alone.
A common starting point is one ton of cooling for every 400 to 600 square feet. But that rule is only a rough estimate, and getting the size wrong in either direction creates real comfort and efficiency problems.
Here is how to figure out the right size for your home, and which Goodman units match each tonnage.
How AC Sizing Actually Works
Air conditioner size is measured in tons, and one ton equals 12,000 BTUs of cooling capacity per hour. It has nothing to do with weight - it is simply a measure of how much heat the system can remove from your home.
Here is how tonnage lines up with BTUs:
- 1.5 ton = 18,000 BTU
- 2 ton = 24,000 BTU
- 2.5 ton = 30,000 BTU
- 3 ton = 36,000 BTU
- 3.5 ton = 42,000 BTU
- 4 ton = 48,000 BTU
- 5 ton = 60,000 BTU
The easiest way to think about it is this: a bigger number means more cooling capacity, but more capacity is not automatically better. The goal is to match the system to the actual heat load of your home.
AC Sizing Chart by Square Footage and Climate
This chart gives you a realistic starting range. Homes in hot, humid climates generally need more capacity per square foot than homes in cooler, drier regions.
| Home Size | Cool / Moderate Climate | Hot / Humid Climate |
|---|---|---|
| 600 - 1,000 sq ft | 1.5 ton | 1.5 - 2 ton |
| 1,000 - 1,300 sq ft | 2 ton | 2 - 2.5 ton |
| 1,300 - 1,600 sq ft | 2.5 ton | 3 ton |
| 1,600 - 1,900 sq ft | 3 ton | 3 - 3.5 ton |
| 1,900 - 2,200 sq ft | 3.5 ton | 4 ton |
| 2,200 - 2,600 sq ft | 4 ton | 4 - 5 ton |
| 2,600 - 3,200 sq ft | 5 ton | 5 ton (may need two systems) |
Treat this as a starting point, not a final answer. Two homes with identical square footage can need different equipment depending on insulation, window count, ceiling height, and how much direct sun they take.
Why Bigger Is Not Better
The most common sizing mistake is going too large. It feels safe - more power, faster cooling. In practice, an oversized system creates more problems than an undersized one.
An oversized air conditioner cools the air quickly, then shuts off before it has run long enough to pull humidity out of the home. This is called short cycling. The result is a house that feels cold and clammy at the same time.
Short cycling also causes other issues:
- Uneven temperatures from room to room
- Higher energy bills from frequent starts and stops
- More wear on the compressor, which shortens system life
- Poor humidity control, which invites mold and discomfort
This matters because comfort is about more than temperature. A right-sized system runs longer, quieter cycles that actually dehumidify the air - which is exactly what you want in a hot, sticky summer.
What Happens If the System Is Too Small
An undersized unit has the opposite problem. It runs almost constantly on hot days and still struggles to hit the thermostat setting.
That constant running drives up energy bills and wears the equipment out faster. On the hottest afternoons - exactly when you need it most - an undersized system simply cannot keep up.
The goal is the middle: a system sized to run steady, complete cycles that cool and dehumidify without either short cycling or running nonstop.
Replacing an Existing System? Start With the Same Size
If you are replacing a system that has worked well, the safest move is to stay with the same tonnage - unless something about the home has changed.
Reasons to reconsider size include:
- A home addition or finished basement that added conditioned space
- New insulation, windows, or air sealing that reduced your heat load
- An old system that was already the wrong size to begin with
If none of those apply and your current system kept the house comfortable, match the tonnage. A previous contractor most likely sized it correctly, and jumping up a size "for good measure" is how oversizing problems start.
When to Get a Manual J Load Calculation
Charts get you close. A Manual J load calculation gets you exact.
Manual J is the industry-standard method for calculating a home's true heating and cooling load. It accounts for square footage, insulation, window type and placement, orientation, ceiling height, local climate data, and more.
For a straightforward replacement in an unchanged home, matching your existing size is usually enough. For a new build, a major renovation, or any home where the current system never felt right, a Manual J calculation is worth requesting before you buy.
A Note on Coil Matching
Once you land on a tonnage, the outdoor condenser needs to be paired with the right indoor equipment - an evaporator coil with a blower, an evaporator coil with a furnace, or an air handler that contains both.
The pairing should be an AHRI-matched combination, not just a tonnage-for-tonnage guess. A 3-ton condenser does not strictly require a 3-ton coil; depending on the system, it can be matched with a larger coil to improve efficiency. Always follow the AHRI-matched pairing rather than assuming identical tonnage on both sides.
SEER2 Efficiency: What to Buy for Your Region
Once size is settled, efficiency is the next decision. Federal SEER2 minimums depend on where you live:
- North: 13.4 SEER2 minimum
- South and Southwest: 14.3 SEER2 minimum
Here is the practical recommendation. In the North, stepping up to a 14.3 SEER2 unit is worth the small premium for the added efficiency. In the South, where 14.3 is already the floor, moving up to the 15.2 SEER2 tier (the GLXS5 series) typically pays back through lower summer bills in a climate that runs the AC hard for months.
Goodman Units by Tonnage
Once you know your size and efficiency tier, matching a Goodman unit is straightforward. The chart below shows approximate equipment price ranges by tonnage. Installation labor is separate.
| Tonnage | Goodman Series (SEER2 Tier) | Est. Equipment Price |
|---|---|---|
| 1.5 - 2 ton | GLXS4 (14.3) / GLXS5 (15.2) | $1,750 - $2,400 |
| 2.5 - 3 ton | GLXS4 (14.3) / GLXS5 (15.2) | $2,300 - $3,100 |
| 3.5 - 4 ton | GLXS4 (14.3) / GLXS5 (15.2) | $2,900 - $3,600 |
| 5 ton | GLXS4 (14.3) / GLXS5 (15.2) | $3,400 - $3,950 |
Current Goodman condensers run on R-410A or the newer R-32 refrigerant, depending on the model. If you are replacing an older R-410A system, keep in mind that R-32 equipment is not cross-compatible - a refrigerant change almost always means replacing both the indoor and outdoor equipment as a matched set.
For a full breakdown of installed pricing on a specific size, see our guide on 3 ton AC unit cost. If you are still weighing the brand itself, our honest take on whether Goodman is a good brand covers reliability, warranty, and value.
Frequently Asked Questions
How many square feet will a 3 ton AC cool?
A 3 ton system typically cools roughly 1,300 to 1,900 square feet, depending on climate and insulation. In hot, humid regions it covers the lower end of that range; in cooler climates it can handle the upper end.
Is it better to oversize or undersize an AC?
Neither. An oversized unit short cycles and leaves the home humid, while an undersized unit runs constantly and struggles on hot days. A correctly sized system that runs steady, complete cycles is always the goal.
Can I just replace my old AC with the same size?
Usually yes. If your current system kept the home comfortable and nothing about the house has changed, matching the existing tonnage is the safest choice. Only reconsider the size if you have added space, upgraded insulation, or the old system was never sized correctly.
Do I need a professional load calculation?
For a like-for-like replacement in an unchanged home, matching your current size is generally sufficient. For new construction, major renovations, or a home that was never comfortable, a Manual J load calculation gives you the precise number.
Does a higher SEER2 rating change what size I need?
No. SEER2 measures efficiency, not capacity. A 3 ton unit delivers 36,000 BTUs whether it is 14.3 or 15.2 SEER2 - the higher rating simply uses less energy to do it.
The Bottom Line
Getting AC size right is about matching capacity to your home's real cooling load - not guessing high to be safe. Use the chart to find your starting range, adjust for your climate and insulation, and stay with your current size on a straightforward replacement.
Once you know your tonnage, match it to the right SEER2 tier for your region and pair the condenser with an AHRI-matched coil or air handler. Get those three things right, and the system will run efficiently and comfortably for years.
Price ranges reflect current market estimates and should be verified against live inventory and your contractor's installed quote before purchase.