What Size Central Air Conditioner Do I Need

If you live in a warmer climate, you can’t do without an AC. However, having a central AC does not guarantee comfort, especially during summer. You must get the size right. A unit that’s too small will work harder to cool the space and will be inefficient, leading to higher energy bills.

Also, you cannot expect sufficient cooling.

On the other hand, a central AC that is too large for the space will go on and off too frequently, resulting in higher running costs. Short cycling also causes faster wear and tear, minimizing the lifespan of your unit. And that’s not all; you will have to contend with high humidity.

You must be wondering, “How many BTU central air conditioner do I need?” Wonder no more. In this article, we will show you a quick way to estimate what size you need. We will also demonstrate how to use our calculator to get a more accurate answer.

Size Difference: Central AC vs. Portable AC/Window AC

A central air conditioner is large, ranging from 18,000 to 60,000 BTU. As a result, this unit is suited for cooling the entire home. It is also the best system for removing humidity.

On the other hand, a portable or window AC usually ranges between 5,000 and 15,000 BTU. Its low capacity is only adequate for cooling one room. You will need one in each room to cool the entire house.

The Estimation Method

Question 1: What Ton Air Conditioner Do I Need? (With Estimation example)

This question often comes to mind when you decide to install a new central ac. First, let’s use the fastest and easiest way to estimate how many tons of central air conditioner your house needs.

Based on the estimation method, the rule of thumb in the HVAC industry is 20 BTU per square footage.

To calculate what size unit central ac you need, multiply the total square footage of your house by 20. You can get the total area of the entire building by multiplying the length and width of each room and adding them up.

Here is an example demonstrating how to estimate the size of a central air conditioner using the rule of thumb.

Question: What size air conditioner do I need for a 2,400 sq. ft. house?

Answer: We will multiply the total square footage of the room by 20 BTU (rule of thumb). 2,400 times 20 BTU is 48,000 BTU.

But the question is “what ton air conditioner do I need”. So, we need to know how many tons of ac you need per square foot.

To get the measurement in Tonnage, you should divide the total result by 12,000 BTU because 1 ton equals 12,000 BTU.

Let’s look at the calculation:

Given a room size of 2,400 sq. ft., how many BTU air conditioner do I need?

2,400 sq. ft. X 20 BTU per sq. ft. = 48,000 BTU

How do I know how many tons my air conditioner is?

48,000 BTU ÷ 12,000 BTU = 4 tons

In short, for a 2,400 sq. ft. house, you need a 4 tons central air conditioner, which is 48,000 BTU.

Table 1: What size air conditioner do I need for various size houses?

In order to get the answers you want directly, we have provided some central air conditioner sizes suitable for common house sizes in the United States. The table below shows the size of the room in square feet and corresponding central air conditioner sizes.

Room Square FootageRecommended Size (Ton)Convert to BTU
900 sq ft house1.5 Ton18,000 BTU 
1,000 sq ft house1.5 - 2 Ton20,000 BTU
1,200 sq ft house2 Ton24,000 BTU
1,300 sq ft house2 Ton26,000 BTU
1,500 sq ft house2.5 Ton30,000 BTU
1,800 sq ft house3 Ton36,000 BTU
2,000 sq ft house3 - 3.5 Ton40,000 BTU
2,200 sq ft house3.5 - 4 Ton44000 BTU
2,400 sq ft house4 Ton48,000 BTU
3,000 sq ft house5 Ton60,000 BTU
5,000 sq ft house5 Ton100,000 BTU

If your house is similar in size to the reference data provided in the chart above, you can get the central ac size answer directly. But if you can’t get the exact square footage of your house on the table, go for the closest option.

For example, let’s assume your house is 2,500 sq. ft. The closest size to that on the chart is 2,400 sq. ft.

Based on the chart, a 2,400 sq. ft. house needs a 4 tons or 48,000 BTU central ac. So, this is the best reference when choosing your air conditioner size.

Question 2: How big is My Central AC? (With Estimation example)

There are many central ac units in the market. But with so many different size options, you can easily get confused.

How big is this central ac? How many square feet can this central ac cool? Which size should I choose? These are some of the questions that often come to mind.

Using the rule of thumb, it is possible to quickly deduce how many square feet a central air conditioner can cool.

We will demonstrate using an example:

Question: How many square feet does a 3 ton air conditioner cool?

Answer: For calculation purposes, we first need to convert tonnage to BTU. One ton equals 12,000 BTU. So, we need to multiply the tons by 12,000 BTU to get the size in BTU/hour.

In this case, the calculation is as follows: 3 tons X 12,000 BTU =36000 BTU.

Given that the central air conditioner is 36,000 BTU, we can calculate the size of the house using the Rule of Thumb. Again, the rule of thumb is 20 BTU per square footage. So, you should divide 36,000 by 20.

The calculation is as follows: 36,000 BTU ÷ 20 BTU per square footage =1,800 square feet room size.

Table 2: How Many Square Feet Can the Central AC Cover?

The table below details the capacity of the central AC and the room size they can cover in square feet.

Central Air Conditioner SizeTons Convert To BTUsHow Many Square Feet Does My Central Air Conditioner Cover?
1.5 ton central air conditioner18,000 BTUs900 sq ft
2 ton central air conditioner22,000 BTUs1100 sq ft
2.5 ton central air conditioner30,000 BTUs1500 sq ft
3 ton central air conditioner36,000 BTUs1800 sq ft
3.5 ton central air conditioner42,000 BTUs2100 sq ft
4 ton central air conditioner48,000 BTUs2400 sq ft
5 ton central air conditioner60,000 BTUS3000 sq ft

The seven sizes of central air conditioners listed on the table above are the most common on the market.

How big is a 1.5 ton central air conditioner?

As you can see from the table, 1.5 tons equals 18,000 BTU. A 1.5 tons central AC can cool a 900 square feet room.

The Accurate Method (Central AC Size Calculator)

Although the estimation method is quick, it will not give you an accurate result. That’s because it does not consider other factors apart from room size. The Air Conditioning Contractors of America (ACCA) recommends using the Manual J method.

The Manual J is a process that allows you to assess your home’s heating and cooling needs accurately. Unlike the rule of thumb, it takes into account additional factors such as:

  • Number of windows
  • Ceiling height
  • Type of roof
  • Condition of the insulation
  • Number of people in the house
  • Heat generating devices
  • Ventilation

However, the Manual J method requires the use of professional software. A contractor will then turn to Manual S after determining the total cooling load in your house. The protocol guides them in deciding what size of equipment you will buy.

Using Our Central Air Conditioner Sizing Calculator

Fortunately, our central air conditioner size calculator simplifies the Manual J process for you. It offers you a quick way to determine the size of the central AC unit you need by considering the following factors.

Central AC BTU Calculator by Square Footage

sq ft

Home Size

The bigger the house, the larger the AC unit required. In the calculator, you will need to manually fill in the size of your home in square feet.

Climatic Region

The climatic region is another important factor that will affect the size of your AC. For instance, hot areas will need a large-sized AC to regulate the temperature.

There are many ways to divide climatic regions. We use 7 levels of climate zones as briefly described below. In the calculator, you should select the region your area falls from the drop-down menu.

US climate zones recognized by Building America in the continental United States.

IECC climate zone map


Hot-humid regions have high temperatures and humidity. They get 20+ inches (50+ cm) of annual precipitation. And they can experience temperatures as high as 73+°F for 1500+ hours in a month.

It includes Climate Zone 1, 2 and 3.


Areas that fall in this climatic zone get 20+ inches (50+) cm of precipitation yearly. Additionally, the number of heating degree days is roughly 5,400. The outdoor temperature also drops as low as 45°F in the winter months, on average.

It includes Climate Zone 4 and 3.


The annual precipitation in this climatic region never exceeds 20 inches (50 cm). Also, the monthly average outdoor temperature never falls below 45°F (7°C) all year round.

It includes Climate Zone 2 and 3.


Areas in this climatic region have the same number of heating degree days as in the mixed-humid climatic region. Their winter months’ average outdoor temperature is also less than 45°F (7°C). However, the annual precipitation it receives is below 20 inches (50 cm).

It includes Climate Zone 4.


Areas in cold climatic regions get 5,400 to 9,000 heating degree days (65°F basis).

Include Climate Zone 5 and 6.

Very Cold

An icy climatic region experiences 9,000 to 12,600 heating degree days (65°F basis).

It includes Climate Zone 7.


An area should meet specific criteria to be a marine climatic region. That includes having a coldest month mean temperature that ranges from 27°F to 65°F and the warmest month mean temperature not exceeding 72°F.

It includes Climate Zone 3 and 4.

We provide a very specific table for the different cooling capacities required in different climate zones. Please check Table 3 below.

Insulation Grade

Insulation assists in regulating the temperature in a building. However, it needs to be in good condition to function effectively.

There are three options to choose from in the calculator depending on the year your house was completed. Choose one.

  • Good (after 2000)
  • Average (1975 – 2000)
  • Bad (before 1975).

Sun Exposure

A house exposed to the sun for longer will gain a lot of heat. Therefore, you will need a high capacity central AC to keep it cool. Determine the amount of sun exposure in your area and choose one among the three options:


Areas with good sun exposure get between 3200 and 4000 hours of annual sunshine.


Regions that receive average sunshine exposure get between 2400 to 3200 hours of sunshine per year.


If your area gets inadequate sunshine exposure, it will receive between 1600 to 2400 hours of annual sunshine.

Number of Doors and Windows

Windows and doors are potential outlets for letting heat in and out. The more they are in your house, the harder your AC will need to work.

There is a separate box for the windows and doors. Count the number of each and fill the results in the respective boxes.

Question 3: What size air conditioner do I need for 1500 square feet?

This time we’ll see how to use our calculator to accurately figure out the size of a central air conditioner for 1,500 sq. ft. of space.

Here is the answer:

Here are the factors we are working with in this example:

  • Climate Zone: Zone 5
  • Home Size: 1,500 sq. ft.
  • Insulation Grade: Average
  • Sun Exposure: Average
  • Amount of Windows: 6
  • Amount of Doors: 1

As you can see from the picture, the calculator’s recommended size for a central air conditioner is 24,000 – 36,000 BTU, which converts to 2 – 3 tons.

Table 3: Cooling BTUs per Square Footage for 7 Climate Zones

The following table shows the cooling capacity size range per square footage for a central AC for different U.S. climatic regions.

Climate ZoneCooling BTUs Per Square Footage
Climate Zone 1 & 2 (hot)22-30 BTUs / Sq. Ft.
Climate Zone 3 (warm)20-24 BTUs / Sq. Ft.
Climate Zone 4 (moderate)18-22 BTUs / Sq. Ft.
Climate Zone 5 (cool)16-20 BTUs / Sq. Ft.
Climate Zone 6 (cold)14-18 BTUs / Sq. Ft.
Climate Zone 7 (very cold)12-16 BTUs / Sq. Ft.

Table 4: Cooling BTUs for Various Room Sizes in 7 Climate Zones

The following table shows the cooling capacity needed for different room sizes in varying climatic regions.

Climate Zone - CoolingSquare FootageCooling BTUs NeededCooling Zone Example Areas
Climate Zone - Cooling1 sq ft22-30 BTUs / Sq. Ft.Cooling Zone Example Areas
Climate Zone 1&2600-820 sq ft18000 BTUHawaii, Miami, Houston
800-1100 sq ft24000 BTU
1000-1400 sq ft30,000 BTU
1200-1650 sq ft36,000 BTU
1400-1900 sq ft42,000 BTU
1600-2200 sq ft48,000 BTU
2000-2800 sq ft60,000 BTU
Climate Zone 31 sq ft20-24 BTUs / Sq. Ft.Atlanta, Los Angeles, Las Vegas
750-900 sq ft18000 BTU
1000-1200 sq ft24000 BTU
1250-1500 sq ft30,000 BTU
1500-1800 sq ft36,000 BTU
1750-2100 sq ft42,000 BTU
2000-2400 sq ft48,000 BTU
2500-3000 sq ft60,000 BTU
Climate Zone 4 (moderate)1 sq ft18-22 BTUs / Sq. Ft.Baltimore, Albuquerque, Seattle
820-1000 sq ft18000 BTU
1100-1400 sq ft24000 BTU
1400-1700 sq ft30,000 BTU
1600-2000 sq ft36,000 BTU
1900-2400 sq ft42,000 BTU
2200-2700 sq ft48,000 BTU
2700-3300 sq ft60,000 BTU
Climate Zone 5 (cool)1 sq ft16-20 BTUs / Sq. Ft.Chicago, Boulder
900-1125 sq ft18000 BTU
1100-1400 sq ft24000 BTU
1500-1900 sq ft30,000 BTU
1800-2250 sq ft36,000 BTU
2100-2700 sq ft42,000 BTU
2400-3000 sq ft48,000 BTU
3000-3750 sq ft60,000 BTU
Climate Zone 6 (Cold)1 sq ft14-18 BTUs / Sq. Ft.Minneapolis, Helena
1000-1300 sq ft18000 BTU
1300-1700 sq ft24000 BTU
1700-2200 sq ft30,000 BTU
2000-2600 sq ft36,000 BTU
2300-3000 sq ft42,000 BTU
2700-3500 sq ft48,000 BTU
3300-4300 sq ft60,000 BTU
Climate Zone 7 (Very Cold)1 sq ft12-16 BTUs / Sq. Ft.Duluth, Fairbanks
1125-1500 sq ft18000 BTU
1500-2000 sq ft24000 BTU
1900-2500 sq ft30,000 BTU
2250-3000 sq ft36,000 BTU
2700-3500 sq ft42,000 BTU
3000-4000 sq ft48,000 BTU
3800-5000 sq ft60,000 BTU

Question 4: What size air conditioner do I need for a 2,000 sq. ft. house?

First, let us examine the example below to see how it works using the estimation method.

Question: What size air conditioner do I need for a 2,000 sq. ft. house?


As we mentioned before, there are two key conditions, respectively:

20 BTU per square footage (rule of thumb)

1 ton = 12,000 BTU.

Given a room size of 2,000 sq. ft., how many BTU air conditioner do I need?

Step 1: 2,000 sq. ft. X 20 BTU per sq. ft. = 40,000 BTU.

How many air conditioners tons does it equal to?

Step 2; 40,000 BTU ÷ 12,000 BTU = 3.333 tons (3.5 tons)

Secondly, let’s look up the answer in Table 4.

We can see that 1,800-2,250 sq. ft. corresponds to 36,000BTU. This is the answer we got from the table Cooling BTUs for Various Room Sizes in 7 Climate Zones.

Third, let’s take a look at the more precise result that we get when we use our calculator to account for more factors.

In this case, we will assume the house has 6 windows and 2 doors and is located in region 5, which experiences average sun exposure. It was built after 2000 and, therefore, has good insulation.

According to the calculator, the Recommended BTU estimate ranges from 30,000 to 48,000 BTU, which converts to 2.5 – 4 tons.

Final Word

Buying the wrong size central conditioner will lead to ineffective cooling of your house and could increase your electricity bill. We hope this article has made it easier for you to determine the correct size central air conditioner for you. Remember, only hire a professional contractor to install it.

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