Figuring out what size AC you need for your house starts with one rough rule: about 20 BTU of cooling for every square foot, or roughly one ton for every 500 to 600 square feet. That math gives you a ballpark, not a final answer. The real size depends on your insulation, windows, ceiling height, and our Western Arkansas humidity, which is why a professional load calculation beats any chart.
This guide gives you the quick ballpark, then shows you what actually drives the right size, what goes wrong when the size is off, and how a pro pins it down. You can also use the AC Size Estimator at the bottom of this page to get a quick starting range for your own home. Read on before you let anyone sell you a system based on square footage alone.
How Is AC Size Measured?
AC size is measured in tons, and one ton equals 12,000 BTU per hour of cooling. A ton has nothing to do with weight here. It is simply how much heat the system can pull out of your home in an hour.
Residential air conditioners come in half-ton steps, from 1.5 tons up to 5 tons. A 2-ton unit moves 24,000 BTU, a 3-ton unit moves 36,000 BTU, and so on. Anything larger than 5 tons usually means a home needs two systems instead of one. These sizes apply across our air conditioning services, from repair to new installs.
What Size AC Do I Need for My Square Footage?
As a rough starting point, you can estimate what size AC you need by matching your square footage to a tonnage range. Use these numbers as a ballpark only, then have the size confirmed before you buy.
- 600 to 1,000 square feet: about 1.5 tons.
- 1,000 to 1,500 square feet: about 2 to 2.5 tons.
- 1,500 to 2,000 square feet: about 2.5 to 3.5 tons.
- 2,000 to 2,500 square feet: about 3.5 to 4 tons.
- 2,500 to 3,000 square feet: about 4 to 5 tons.
For a quick number tailored to your home, use the AC Size Estimator at the bottom of this page. It takes your square footage along with a few details like insulation and sun exposure, and returns a starting range. In a hot, humid climate like ours, homes often land toward the higher end of each range. Even so, do not treat these numbers as final. Two homes with the same square footage can need very different systems, and the next section explains why.
Why Square Footage Alone Is Not Enough
Square footage alone is not enough because it ignores everything else that lets heat into your home. A tight, shaded, well-insulated house needs far less cooling than a drafty one of the same size with big sunny windows. Sizing on square footage by itself is how homes end up with the wrong system.
Several things shift the real number up or down:
- Insulation and air sealing. A leaky, poorly insulated home needs more cooling.
- Windows. Lots of windows, west-facing glass, or single-pane windows raise the load.
- Ceiling height. Tall ceilings mean more air to cool.
- Sun and shade. Full sun with no shade trees adds heat.
- Ductwork. Leaky or undersized ducts waste capacity before the air reaches you.
Our humidity matters most of all. According to ENERGY STAR, oversized air conditioners short-cycle and do not run long enough to pull moisture out of the air, a problem that hits hardest in hot, humid regions. That is why bigger is not better here. The right size handles both the heat and the Western Arkansas mugginess.
What Happens If My AC Is the Wrong Size?
The wrong size AC causes real comfort and cost problems, no matter which direction it misses. Both too big and too small leave you worse off than a unit sized correctly.
- Too small: the system runs nonstop on hot days and still never quite cools the house. It wears out early from the constant strain.
- Too big: the system cools fast, then shuts off before it removes humidity. Your home feels cool and clammy at the same time, and the rapid on-off cycling, called short-cycling, wears the parts out and drives up your bills.
Most homeowners assume bigger is safer, but an oversized unit is often the worse mistake in our climate. Getting the size right the first time protects your comfort, your wallet, and the life of the system.
Should I Size Up If I Am Between Two Sizes?
If your load calculation lands between two standard sizes, the safer choice is usually the smaller one. Air conditioners only come in half-ton steps, so some rounding is normal. In our humid climate, a slightly smaller unit that runs longer pulls more moisture out of the air and keeps you more comfortable than one that is a half-ton too big.
A good installer will not simply round up to play it safe. They size to the calculated load, then pick the closest standard unit with your comfort and humidity in mind. If anyone tells you bigger is always better, treat that as a reason to get a second opinion.
What Is a Manual J Load Calculation?
A Manual J load calculation is the industry-standard method for sizing an AC to your exact home. Instead of guessing from square footage, a technician measures the things that actually drive your cooling load and runs the numbers through trusted software.
The calculation accounts for your square footage, insulation, windows, ceiling height, sun exposure, ductwork, and local climate. The result is the true cooling load for your home, in BTU, which points to the right tonnage. Our AC installation process always starts with a Manual J calculation, because a system sized to your home runs more efficiently and lasts longer than one sized to a rule of thumb.
How Do I Find the Size of My Current AC?
You can find the size of your current AC by reading the model number on the outdoor unit, not the serial number. Look for a number in the model that is divisible by 12, such as 18, 24, 30, 36, 42, 48, or 60.
Divide that number by 12 to get the tonnage. A 24 means a 2-ton unit, a 36 means 3 tons, and a 60 means 5 tons. This tells you what you have now, but it does not prove that size was ever right. If your old system always struggled or left rooms muggy, the smart move is a fresh load calculation rather than matching the old size by default.
Get the Right Size AC in Fort Smith
Try the AC Size Estimator below for a quick ballpark, then reach out to Riverside when you want the right size AC chosen by measurement, not by guesswork. Our veteran-owned team runs a full load calculation, inspects your ductwork, and walks you through your options in plain language across Fort Smith, Van Buren, and Greenwood. If your home has additions or rooms that never cool evenly, we can also talk through ductless mini-split systems that cool zones independently.
Ready to size your system the right way? Contact Riverside Heating Air Plumbing to schedule your in-home assessment today.
AC Size Estimator
Get a rough tonnage range for a Western Arkansas home. This is a starting point, not a final size. Only a Manual J load calculation gets it exactly right.
This estimator gives a rough range based on square footage and a few factors. It is not a substitute for a Manual J load calculation, which measures insulation, windows, ductwork, and more. No prices are shown.
