Mini Split Sizing Calculator: How Many BTU Mini Split Do I Need?

Adequately sizing a mini split is crucial. We have prepared a Mini Split Sizing Calculator to enable anybody to estimate how many BTU mini split you need. On top of that, you will also find a chart for mini split sizes for 300 to 5,000 sq ft (6,000 BTU to 100,000 BTU).

Namely, with the mini split sizing, you want to avoid these two things:

• Undersized mini split. This will leave your home hot (75°F or more) and humid. Example of an undersized mini split: Using a 12,000 BTU mini split for an 800 sq ft area.
• Oversized mini split. If the ductless mini split is too big, it will short cycle, causing unwanted hot pockets, not tackling humidity as it should, and shortening the lifespan of a more-expensive-than-needed mini split AC. Example of an oversized mini split: Using a 12,000 BTU mini split for a 200 sq ft area.

Now, there are two ways how to correctly size a mini split:

1. Rough Estimation. This is what we will do here with the help of the mini split sizing calculator (to get an idea of how big a mini split you need). We will use 4 factors – square footage and ceiling height, sun exposure, climate, and inclusion of kitchen – to calculate how many BTU mini split you need.
2. Manual J Calculation. This is what a hands-on HVAC technician will use to estimate the mini split BTU size. In addition to the 4 factors above, it also accounts for insulation (R-values), size and number of windows, and so on.

Before you use the mini split sizing calculator, let’s manually solve a 1,000 sq ft example to illustrate how to adequately size a mini split, based on the BTU per square foot rule of thumb:

How Many BTU Per Square Foot For A Mini Split? (+ 1,000 Sq Ft Example)

Split-system AC sizing rule of thumb we use in HVAC is this:

You need 20 BTU per square foot cooling output (standard 8 ft ceiling height).

Example: 600 sq ft room would need a 12,000 BTU mini split, since 600 sq ft × 200 BTU/sq ft = 12,000 BTU.

Now, we have to account for all of these factors (in accordance with the Energy Star guidelines):

1. 20 BTU per sq ft for 8 ft ceiling height. For every additional foot of ceiling height, we have to add 12.5% to the total mini split BTU estimate.
2. Sun exposure. For heavy sun exposure, we add +10% BTUs. For low sun exposure (heavily shaded), we subtract -10% BTUs.
3. Climate. If you live in a very hot state (Florida, California, Texas), we add 10% BTUs. For cooler states (Minnesota, New York, Illinois), we subtract -10% BTUs.
4. Kitchen inclusion. If you are sizing a ductless mini split for the kitchen, add 4,000 BTU. This is because there are a lot of heat-generation appliances like ovens, dishwashers, toasters, etc. in the kitchen, and we need additional cooling output just to be safe.

Let’s look at this example: How many BTU mini split do you need for 1,000 sq ft area? Let’s say we have a 9 ft ceiling height (+12.5%), heavy sun exposure (+10%), normal climate (Tennessee), and that the area includes the kitchen (+4,000 BTU).

Here is how we will calculate the size of mini split for this situation:

1,000 Sq Ft Mini Split Size = 1,000 Sq Ft × 20 BTU/Sq Ft × 1.125 (Ceiling Correction) × 1.1 (Sun Exposure Correction) × 1 (Normal Climate) + 4,000 BTU = 28,750 BTU

In this case, we need a net cooling output of 28,750 BTU. Practically, we would install a 3-zone mini split with two 9,000 BTU air handlers and one 12,000 BTU air handler for a net cooling output of 30,000 BTU (very close to our 28,750 BTU target).

This is just one example. You might have a 500 sq ft room or a 2,000 BTU house, low or heavy sun exposure, live in California or New York, and so on. As you can see, all these manual calculations can be a bit complex, right?

That’s why we have prepared the following mini split BTU calculator you can freely use. You just insert room size, ceiling height, sun exposure, and so on, and the calculator will tell you how big a mini split you need.

Below the calculator, we have also prepared a mini split sizing chart that estimates how many square feet can different mini split cover adequately:

Mini Split Sizing Calculator (Calculate Mini Split BTUs)

To illustrate how this mini split size calculator works, let’s solve one example:

Let’s say you have a 500 sq ft place with a 10 ft ceiling height, heavily shaded, in the southern US, and it doesn’t include the kitchen. What size mini split for you need for a 500 sq ft room with these specifics? Just slide the 1st square footage slider to ‘500’, the 2nd ceiling height slider to ’10’, specify ‘Heavily Shaded’ sun exposure, ‘Hot’ climate, and ‘No’ on kitchen inclusion. We get the result:

For this 500 sq ft area, we need a 12,375 BTU of cooling output. In this case, you can opt for a 12,000 BTU 1-zone mini split (close to our 12,375 BTU target).

Here is the mini split AC size chart for 300 sq ft to 5,000 sq ft areas, based on the basic 20 BTU per sq ft HVAC rule of thumb. We have also included the recommended 6,000 BTU, 9,000 BTU, 12,000 BTU, and 15,000 BTU mini split air handler combinations in the last column, and mini split tonnage for everybody wondering how many ton mini split you need:

Mini Split Size Chart

With this mini split BTU size chart, you now have a good idea of what size ductless mini split you need. For bigger spaces, you will have to go with 2-zone, 3-zone, 4-zone, 5-zone, 6-zone, 7-zone, 8-zone, or even 9-zone mini split.

Alternatively, you can use a bigger 18,000 BTU, 24,000 BTU, 30,000 BTU, or 36,000 BTU mini split air handler. Just keep in mind that you will have to facilitate the airflow to several rooms (open doors for homogeneous cooling coverage).

This is the 101 on mini spit AC sizing. If you need a bit of advice, you can give us some figures in the comment section below, and we will help you out. Thank you.