AC Tonnage Calculator Per Square Foot (+Tonnage Table)

Before buying an air conditioner, you have to make the AC tonnage calculation. Not sizing an AC unit properly can cause $100s in wasted unit costs or future electricity costs. 

According to the DOE,

“…an air conditioner generally needs 20 BTU for each square foot of living space.”

We need to convert BTU to tonnage. 1 ton equals 12,000 BTU. That means that, on average, we will need 0.0016 tons per square foot

To properly get the tonnage of the AC you need, you can use the AC tonnage calculator here:

Calculated Tonnage:

0.00 Tons

 

For example, a standard 1,500 sq ft house would need a 2.5-ton air conditioner. To help us out, here is a quick table showing how many tons (and BTU) air conditioners we need for certain square footage:

Tonnage Table

Area (Square Feet): BTU Tonnage
600 sq ft 12,000 BTU 1 Ton
900 sq ft 18,000 BTU 1.5 Tons
1,200 sq ft 24,000 BTU 2 Tons
1,500 sq ft 30,000 BTU 2.5 Tons
1,800 sq ft 36,000 BTU 3 Tons
2,100 sq ft 42,000 BTU 3.5 Tons
2,400 sq ft 48,000 BTU 4 Tons
2,700 sq ft 54,000 BTU 4.5 Tons
3,000 sq ft 60,000 BTU 5 Tons
3,300 sq ft 66,000 BTU 5.5 Tons
3,600 sq ft 72,000 BTU 6 Tons

Here is the most frequently asked question about tonnage, BTU, and area (square footage):

How Many Tons Of AC Per Square Foot? (Tonnage Per Square Foot)

Simple answer: You need 0.0016 tons of AC per square foot.

In short, if you’re looking to cool down a 600 sq ft area, you would need:

AC Capacity = 600 sq ft * 0.0016 tons/sq ft = 1 Ton

In general, for every 600 sq ft, you need 1 ton of AC. This is a general estimate.

You can use the ‘tonnage per square foot’ formula to calculate how many tons of AC you need. Here is the formula:

AC Capacity (Tonnage) = (INSERT AREA IN SQ FT) * 0.0016 tons/sq ft

You can insert the area and calculate how many tons of AC you need per certain square footage.

When you calculate the tonnage, you can check out several 1-4 ton mini-split air conditioners here:

Hope this helps. If you have any questions, you can pose them in the comments below.

27 thoughts on “AC Tonnage Calculator Per Square Foot (+Tonnage Table)”

  1. 12/19/2020
    I live in the Dallas, TX area
    My A/C unit is 3.5 tons
    We have 18″ and 9″ return ducts to the upstairs unit.
    My house was built by Ryland, square footage is 2661 and insulated well.
    Although there are hot & cold spots in the house, typically in rooms with large windows, our unit does not run all the time in winter or summer and has lasted 11 years so far.

    Based on the tables & calculations I can find online, my unit should be somewhere between 4.5 tons and almost 6 tons.

    I would expect an under-spec’d system to run all the time just trying to keep up. But ours does not. We had an A/C service come out recently and he suggested that we add more return ducts.

    I am trying to grasp what the symptoms are when the unit is under-sized. I would have expected the unit to burn out long before now if it was working to too hard.

    What am I missing?

    Reply
    • Hello Greg, you have sound reasoning. There are two potential symptoms of under-sized units: not sufficient cooling, and a shorter lifespan of the AC unit. Your cooling is sufficient and the modern ACs are made to last 20 years even if you run them on 100% all the time (regular maintenance is required). Given your situation, you will probably have very little symptoms of these sorts. In short, you’re not missing anything. Hope this helps.

      Reply
    • If you have one 3.5 ton unit for a two-story production built home of 2661 sqft I’d have a HVAC contractor or mechanical engineer run it through the manuals for size and air flow. Well worth the money to be comfortable and efficient.

      Reply
  2. I bought a 15 year old two story home in Houston. My appraisal shows the house is 4300 sqft (2400 on first floor and 1900 on second floor). There’s high open ceiling from entrance all the way through the living room. Property faces west, so it gets a lot of evening sun in the front. The house has tall high ceiling glass windows in the back, but the morning sun in the back is partly shaded by high a ceiling patio. The house seems to have good insulation (but it is 15 years old). The house has the original system installed by the builder with two 3 ton units (Evaporator coils were changed in 2013). I am about to replace this system. Is this tonnage adequate for this house? Should I go to a 4 ton/3.5 ton combo or perhaps a 5 ton/4 ton combo? At what point do we run into the problems of an oversized AC?

    Reply
    • Practically, the tonnage is sufficient if your home was sufficiently cool in the summer. Theoretically, 1 sq ft requires, on average, 20 BTU. 4300 sq ft translates to 86,000 BTU, or about 7.2 tons. Add Houston climate, high ceilings, and subtract good isolation and you’re looking at about 8 tons.

      Oversized ACs are more expensive to buy and install; that’s the only major drawback. Hope this helps.

      Reply
    • Hello Joseph, according to EPA’s recommendation, you would need 20 BTU per 1 sq ft. That means about 20,000 BTU. 12,000 BTU equals 1 ton. The safe bet would be to buy a 2-ton unit (24,000 BTU in total).

      Reply
  3. I have a commercial space rented as a barbershop with aprox 6-7 workers at a time and about 6-10 customers in the shop at a time during peak hours. The space currently has a 6ton ac unit. The space is only 1200 sq ft and a floor to ceiling about 12ft. Will a 3.5-4 ton unit be enough to properly cool my shop?

    Reply
    • Hello Isa, 4 ton (48,000 BTU) unit should be theoretically enough to cool down spaces up to 2,400 sq ft. In practice, the Energy Star guide recommends that you add 600 BTU per person. Let’s say you have 17 people in the shop, that would be 17*600 BTU = 10,200 BTU. So, you still have about 38,000 BTU left; that’s more than enough to adequately cool down your shop.

      Reply
  4. Must a/c condensers be placed w/I 2 feet of house, or can they be more remote?
    I would like them placed away from the house, but do not know if that is possible without problems.

    Reply
  5. Could you help me with Line-set or AC refrigerant line sizes ??
    3 ton AC unit waiting for electric run of 30 amp 220volt , but some knuckle head ran a 20amp yellow romex and what seems to be about a 3/4 line set, could be smaller maybe a 5/8 line set
    on 2nd deck patio , 2 floor to be AC’d is about 1800 sq ft
    I think the line set is to small
    The electric is definitely to small
    Nameplate rating is 25.7 amps

    Reply
    • Hello Micheal, sure thing. Well, if you need a 30 amp, 25.7 amps won’t cut it. It’s hard to talk about the specific situation but a 3 ton AC usually has a 3/4 line set. Hope this helps.

      Reply
  6. I LIVE IN THE CHICAGO AREA AND AM GOING TO REPLACE MY AC I NOW HAVE A 3 1/2 TON COMPRESSOR THE SALESMAN SAYS THAT ALL WE NEED IS 2 1/2 TON I FEEL THAT IT MIGHT BE TO SMALL FOR OUR 1800 SQUARE FOOT HOUSE WE ON A SLAB WHAT IS THE CORRECT SIZE TO INSALL LOOKING AT 16 SEER

    Reply
    • Hello Ray, for the Chicago area, 2 1/2 ton unit (30,000 BTU) just might be enough. 3 1/2 ton unit (42,000 BTU) might be overkill for 1,800 sq ft in Chicago. In Florida, for example, that would be adequate.

      Reply
  7. Hi,

    I am sizing units for a commercial space of approximately 2500 sq feet with 14 foot ceilings. It will be a store so I anticipate no more than 20 people present at a time. But, the previous system was a 10 ton unit connected to three ducts. A new A/C contractor suggested I instead install three 4 ton units, each running off one of the ducts (They do cover the space in zones). He claims that will be more cost-efficient and avoid needing something called an “economize.” Does this make sense? Thanks

    Reply
    • Hello Lydia, the combined cooling output of three 4 ton units will be 12 tons; that’s sufficient cooling output for your situation. 4-ton units can be more energy-efficient than 10-ton units; you can get a lot of 4-ton units with 20+ SEER rating (here are some examples of 4-ton central air conditioners with SEER and costs).

      “Economize” is not an expression we in HVAC are familiar with. The best thing would be to ask what is the SEER rating on 4-ton and 10-ton units. If the difference in SEER rating is about 2 or greater, go with that unit. Example: If a 10-ton unit has 18 SEER, and 4-ton units have 20 SEER, go with 4-ton units. Hope this helps.

      Reply
  8. Hi,

    I am looking to add an A/C unit to a warehouse space, 4700 sq ft with 20 ft ceilings, 1 over head door to be opened 4-5 times a day for a minute or so, 3 employees, in a cold climate (Minnesota) so it will only be running 3-4 months out of the year. What size tonnage unit shoud I be looking at? Thank You.

    Reply
    • Hello Jeff, that’s a huge warehouse with 20 ft ceilings. To calculate the AC tonnage required, you can follow the ’20 BTU per 1 sq ft (8 ft ceiling)’ rule of thumb. So 4700 sq ft * 20 BTU = 235.000 BTU or about 20 tons; but that’s if you would have 8 ft ceilings. You have a 20 ft ceiling; you need to add an additional 150% to that calculation. This would yield a total tonnage of about 50 tons; which is quite a lot. We’re talking about 10 5-ton units for example.

      These calculations, however, might not be as precise when we’re talking about the tonnage required to cool down a large warehouse. We would recommend talking to an HVAC expert on-site. You can call your local HVAC companies or fill in this form and you’ll get some information and free quotes for the warehouse. Sorry, that’s the best we can do; estimating the total tonnage requirements in warehouses is not something we have a lot of experience with.

      Reply
  9. I am in Ohio and have a 1,300 sq. ft. commercial space that is divided up into 6 rooms off a hallway, 1 small bathroom and an entrance area about 8’x15′. There are usually 5-7 people in the space at a time. Currently it has a 3.5 ton roof top ac unit located on the far rear corner. It has about a 25′ run of 12″ diameter flex duct connecting it to the main duct. When temps are above 80 degrees & 50% humidity the unit can not keep the office below 75 degrees and constantly runs. I was quoted to replace it with a 4 ton ac unit centrally mounted on the roof connecting just above the main duct line. Based on the square footage of the space I am concerned that 4 tons is oversized and won’t efficiently remove the humidity. Is this an accurate concern or is more tonnage better?

    Reply
    • Hello John, you have quite a complicated situation here. Calculating the exact tonnage is quite difficult; the best thing to do is to use the 3.5-ton rooftop unit as the benchmark. If that unit doesn’t lower the temperature sufficiently, you need a bigger one; and a 4-ton unit has about 17% higher cooling output than a 3.5-ton unit. There is no concern about overkill here or the consequential short cycling due to 50% humidity. As far as we can see, the 4-ton unit is adequate for this situation.

      Reply
  10. I bought a manufactured home that has 2293 sq ft the company I bought it from installed a 3 ton central unit. Is this unit enough to cool my home? Haven’t moved into the home yet. Please advise me what to do.

    Reply
    • Hello Teresa, it’s hard to say without the additional information, but let’s say we use a rule of thumb ’20 BTU per sq ft’. For a 2293 sq ft home, you would need roughly 2293*20 BTU = 45,860 BTU; this is about 3.8 tons. If you leave in a colder climate (New York, for example), the 3-ton central unit might suffice. If you live in a hot climate (Florida, for example), a 4-ton unit would be a safer option.

      Here is a suggestion: move into the new home and see how well the 3-ton central unit performs. If it doesn’t adequately lower the temperature and humidity, you can always buy an additional window or portable unit as an auxiliary cooling unit.

      Reply
  11. Our house is 1232 sq. feet on a slab with high ceilings in every room going from 8 feet to 12 in some rooms and 16 in others (perhaps the average would be 13 feet?). Our previous AC is 2 ton. It cooled the house ok except on those rare super hot periods. We are in Southeast Iowa. The company for the new AC has ordered a 2.5 ton. Will this be overkill? Do we need 2.5? I do not want the house to become more humid.

    Reply
    • Hello Irene, air conditioners both cool down air and dehumidify it. With a bigger unit, it will become less humid, no worries about that. 2 ton AC unit is, in theory, undersized. For 13 ft ceilings, you would require at least 25 BTU per sq ft. At 1232 sq ft, that would be 30,800 BTU or about 2.5 tons. Even in practice, 2.5-ton seems like a very adequate sizing. Hope this helps.

      Reply
  12. I live in Houston, Texas. The house is 2346 sf, the wall is 9 ft, the sun is everage, the weather is is hot. Based on the two calculations above, the AC should between 4 and 5 tons. The builder installed 5 tons. During the day time, it take 20 minutes to cool the house. At night time, it takes 5 minutes which is a short cycle.
    I think the AC is oversized, do you think so ? It should be better undersized than oversized

    Reply
    • Hello David, for the summer heatwave, the 5-ton unit is a good idea. Short cycling is an indication of an oversized AC unit (with rotary compressors); you can run it at the lowest speed to prevent that from happening. Right now, it might feel like you have an oversized AC but when the heatwave kicks in, you are ready for it. It’s always a problem with the bigger AC systems with a high tonnage cooling capacity.

      Reply

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