AC Tonnage Calculator – What Size Central AC Unit Do I Need

Choosing the correct ac size for your house is imperative. Central air conditioners come in a variety of sizes. They include 1.5 ton, 2 ton, 2.5 ton, 3 ton, 3.5 ton, 4 ton, and 5 ton. Their prices will vary depending on the size and manufacturer.

Choosing the correct size unit for your cooling needs can be challenging with so many options available. One question we always get is, “How big of an ac unit do I need for my house?” If this is you, stick around. We answer this question in detail below.

Estimation Method

What Size AC Do I Need for my House?

The size of your central ac will depend on your home’s cooling needs. Various factors influence that, chief of which is the total area of the house.

One of the easiest ways to calculate how many tons of ac per square foot you need is through the estimation method. It relies on the rule of thumb: 20 BTU per square foot.

The formula is as follows: Area of the house in square foot X 20 BTU

We will demonstrate this using an example.

Question 1: What size air conditioner do I need for a 2,000 sq ft house?

Step 1: Multiply the area by 20 BTU to find how many BTUs you will need to cool a 2,000 sq. ft. room.

2,000 sq ft X 20 btu = 40000 BTU

So, you will need 40,000 BTU to cool a 2,000 sq. ft. room.

You must be wondering, “How do I know how many tons my air conditioner is? That is simple if you know how many BTUs are in a ton.

Step 2: 1 ton equals 12,000 BTU. So, you need to divide 40,000 by 12,000 to get the size of the ac in tons.

40,000 BTU ÷ 12,000 BTU = 3.3 tons.

In short, you will need a 3.5-ton ac to cool a 2,000 sq. ft. room.

AC Tonnage Chart (Tonnage to BTU)

The following table shows the tonnage size of ac units for different room sizes.

AC Tonnage SizeConvert to BTURoom Size (sq ft)
1 ton12,000 BTU600 sq ft
1.5 ton18,000 BTU900 sq ft
2 ton24,000 BTU1,200 sq ft
2.5 ton30,000 BTU1,500 sq ft
3 ton36,000 BTU1,800 sq ft
3.5 ton42,000 BTU2,100 sq ft
4 ton48,000 BTU2,400 sq ft
5 ton60,000 BTU3,000 sq ft

If you know the area of your room, you can figure out how big of an ac unit you need by looking at the chart above.

Example: What size ac unit for 2,400 square feet?

As you can see, the corresponding ac tonnage size on the table is 4 tons. Therefore, you will need a 4-ton air conditioner to cool a 2,400 sq. ft. room.

How Many Square Feet Can My AC Unit Cool?

You will find ac units in a variety of sizes when buying one for your home. How will you know how many square feet each option can cool? You can also find this out using the estimation method. However, you will need to convert tons to BTUs first.

Question 2: How many square feet does a 3-ton air conditioner cool?

Step 1: First, we need to convert the ton to BTU. Since one ton equals 12,000 BTUs, we will multiply three by 12,000 BTU.

3 ton X 12,000 BTU = 36,000 BTU

Step 2: We can calculate how many square feet the ac can cool using the rule of thumb: 20 BTU per square foot. We will divide 36,000 BTU by 20 BTU.

36,000 BTU ÷ 20 BTU = 1,800 square feet

Simply put, a 3 ton air conditioner can cool a 1,800 sq. ft. room.

Using a Tonnage to BTU calculator

If you don’t want to go through all the trouble to convert ton to BTU, you can use our tonnage to BTU calculator.

Question 3: 1.5 ton ac is equal to how many BTU?

Choose 1.5 ton on the drop-down menu.

The answer is 18,000 BTU. You would get the same result through the calculation method.

1.5 ton X 12,000 BTU = 18, 000 BTU

The Accurate Method (Using the AC Tonnage Calculator per Square Foot)

The estimation method is quick. However, it will not give you the most accurate results. That is because it does not take other factors into account.

A professional contractor will use the manual J process when calculating the total cooling load of your house. Apart from size, the process considers other factors such as sun exposure, number of windows, and ceiling height.

Luckily, our ton calculator simplifies the manual J process into a simple DIY tool. You can determine what size of ac your house needs more accurately by following a few steps.

How to Use Our Ac Tonnage Calculator

Our calculator takes several factors into account. They include:

Climate Region

Different climate zones in the US experience varying temperatures and humidity. Therefore, your home’s energy needs will vary depending on your specific climate zone.

Our calculator has seven climatic regions. You can choose the zone you live in from the drop-down menu.

Home Size

We have already established that home size plays a critical role in determining your house’s cooling load. If you have a big home, you will need an ac with a high capacity since the cooling load is high.

Type in the size of your house in square feet in the home size box.

Insulation Grade

The condition of your insulation will also determine the size of your central ac. The ac will have to work harder if the insulation has seen better days. On the other hand, a newly installed insulation will lessen your cooling load.

You have three options on the insulation grade drop-down menu depending on the year you built your home: Good (after 2000), average (1975-2000), and bad (before 1975). Choose the one corresponding to your home.

Sun Exposure

How much sun exposure your house gets will affect the indoor temperature. The more sun exposure you get, the harder your ac will need to work.

Determine the amount of sun exposure your home gets and choose one option from among the three in the drop-down menu: good, average, and bad. Don’t forget to account for things like tree shade.

Amount of Windows and Doors

Are there many windows and doors in your house? These are potential outlets and inlets for heat. The more there are, the more your air conditioner will work to cool the home.

Count the number of windows and doors in your house and fill the results in the respective boxes.

After filling all the boxes, you will see the recommended capacity of your central ac conditioner displayed at the bottom. Let’s use an example to demonstrate.

Example: How to calculate what size air conditioner for 1,500 square feet

In this case, we will work with the following conditions

• Climate Zone: Zone 5
• Home Size: 1,500 sq. ft.
• Insulation Grade: Good
• Sun Exposure: Average
• Amount of Windows: 7
• Amount of Doors: 2

As you can see from the image, the recommended cooling capacity is 2 - 2.5 Ton.

AC Tonnage Chart for Different Climate Zones

The following table displays varying ac tonnage requirements for different climatic zones.

AC Tonnage Size

Convert to BTU

Climate Zones

Best For (sq ft)

1 ton

12,000 BTU

Climate Zone 1 & 2 (hot)

400 - 550 sq ft

Climate Zone 3 (warm)

500 - 600 sq ft

Climate Zone 4 (moderate)

550 - 670 sq ft

Climate Zone 5 (cool)

600 - 750 sq ft

Climate Zone 6 (cold)

670 - 860 sq ft

Climate Zone 7 (very cold)

750 - 1,000 sq ft

1.5 ton

18,000 BTU

Climate Zone 1 & 2 (hot)

600 - 820 sq ft

Climate Zone 3 (warm)

750 - 900 sq ft

Climate Zone 4 (moderate)

820-1,000 sq ft

Climate Zone 5 (cool)

900-1,125 sq ft

Climate Zone 6 (cold)

1,000-1,300 sq ft

Climate Zone 7 (very cold)

1,125-1,500 sq ft

2 ton

24,000 BTU

Climate Zone 1 & 2 (hot)

800-1,100 sq ft

Climate Zone 3 (warm)

1,000-1,200 sq ft

Climate Zone 4 (moderate)

1,100-1,400 sq ft

Climate Zone 5 (cool)

1,100-1,400 sq ft

Climate Zone 6 (cold)

1,300-1,700 sq ft

Climate Zone 7 (very cold)

1,500-2,000 sq ft

2.5 ton

30,000 BTU

Climate Zone 1 & 2 (hot)

1,000 - 1,400 sq ft

Climate Zone 3 (warm)

1,250 - 1,500 sq ft

Climate Zone 4 (moderate)

1,400-1,700 sq ft

Climate Zone 5 (cool)

1,500-1,900 sq ft

Climate Zone 6 (cold)

1,700-2,200 sq ft

Climate Zone 7 (very cold)

1,900-2,500 sq ft

3 ton

36,000 BTU

Climate Zone 1 & 2 (hot)

1,200 - 1,650 sq ft

Climate Zone 3 (warm)

1,500 - 1,800 sq ft

Climate Zone 4 (moderate)

1,600-2,000 sq ft

Climate Zone 5 (cool)

1,800-2,250 sq ft

Climate Zone 6 (cold)

2,000-2,600 sq ft

Climate Zone 7 (very cold)

2,250-3,000 sq ft

3.5 ton

42,000 BTU

Climate Zone 1 & 2 (hot)

1,400 - 1,900 sq ft

Climate Zone 3 (warm)

1,750 - 2,100 sq ft

Climate Zone 4 (moderate)

1,900-2,400 sq ft

Climate Zone 5 (cool)

2,100-2,700 sq ft

Climate Zone 6 (cold)

2,300-3,000 sq ft

Climate Zone 7 (very cold)

2,700-3,500 sq ft

4 ton

48,000 BTU

Climate Zone 1 & 2 (hot)

1,600 - 2,200 sq ft

Climate Zone 3 (warm)

2,000 - 2,400 sq ft

Climate Zone 4 (moderate)

2,200-2,700 sq ft

Climate Zone 5 (cool)

2,400-3,000 sq ft

Climate Zone 6 (cold)

2,700-3,500 sq ft

Climate Zone 7 (very cold)

3,000-4,000 sq ft

5 ton

60,000 BTU

Climate Zone 1 & 2 (hot)

2,000-2,800 sq ft

Climate Zone 3 (warm)

2,500 - 3,000 sq ft

Climate Zone 4 (moderate)

2,700-3,300 sq ft

Climate Zone 5 (cool)

3,000-3,750 sq ft

Climate Zone 6 (cold)

3,300-4,300 sq ft

Climate Zone 7 (very cold)

3,800-5,000 sq ft

Example:How to calculate what size ac unit for 1,200 square feet by calculator & manual method

We will calculate the size of the ac unit using the two methods.

Estimation Method

Step 1: We will use the rule of thumb: 20 BTU per square foot

1,200 sq ft X 20 BTU =24,000 BTU

Step 2: We will convert BTU to tons using the one ton equals 12,000 BTU rule.

24,000 BTU ÷ 12,000 BTU = 2 tons

This answer is similar to that on the ac tonnage chart for different climate zones.

Using the Calculator

We will assume the house is located in zone 5 and has one door and six windows. It also experiences an average sun exposure, and its insulation is average because it was constructed between 1975 and 2000.

According to the calculator, the more accurate answer is 1.5 - 2 Tons

Final Word

Buying the right size central ac will lower your energy bills and increase the lifespan of the unit. Moreover, it will ensure your home is comfortable to live in.

We hope we have made it easier for you to calculate the size of your central ac using the quick estimation method. Remember, you can use our calculator if you want a more accurate result that accounts for various factors.

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