What Size Mini Split System Do I Need? AC Sizing Guide

Mini split air conditioners are a great way to control the temperature in your home. Homeowners favor them over most other AC systems because they work so effectively and are pretty easy to maintain.

However, that effectiveness is dependent on you picking the right mini split for your home.

The size of your mini split will directly impact the overall performance of the unit. This guide will take you through all the considerations and factors so you can pick a mini split that works for you.

Why You Need the Right Size Mini-Split AC

There’s a lot to consider when buying a mini split AC and size can often be overlooked. Many people think that bigger is better or that they can make do with a smaller unit, but it really doesn’t work this way. Without the right size mini split AC system, you just won’t get the same results.

If your mini split is too small, then it won’t be able to heat or cool your home properly. It will run a lot, but you won’t have an even coverage of hot or cold air leading to specific hot or cold spots in your home.

Smaller units will work harder to achieve results, and this, in turn, may lead to higher energy costs. The strain on the ductless mini split will also make it more likely to break down, leading to higher AC repair and maintenance costs.

Having an oversized mini split is the lesser of the two evils, but it still has some downsides. If your mini split is too big, then you might get exaggerated hot and cold temperatures in your room that you don’t want. The unit will also start to short cycle, which means that it runs for short periods and then stops.

This can lead to it being ineffective and can wear it down more quickly, impacting the unit’s longevity. This, in turn, will lead to higher maintenance costs. Of course, the biggest downside to an oversized mini split is that you’ll waste money buying a bigger unit that you just don’t need.

For optimum heating and cooling, you need to get the right size of mini split. This will give you maximum value for money and help you control your home environment effectively.

Related Article What Is A Mini Split?

Factors That Affect Ductless Mini Split AC Sizing

Age and Insulation

Over the past 50 years, building codes have improved, so we have progressively better homes. This means that newer homes have better insulation and will be less impacted by the climate around them.

For newer homes, you won’t need as much heating or cooling power. Basically, if you have an old house, you’ll want more BTUs, and if you have a new home, you’ll want fewer BTUs.

Ceiling Height

Generally, ceilings are about 8ft tall, but in some homes they’re much taller. You need to bear this in mind because it will impact the overall size of the room. If you have tall ceilings, then look to boost your BTUs by 20-30%.

Local Climate

The climate and conditions you live in will determine how hard your mini split AC system needs to work. If you live in a particularly hot or cold place, you need to look for a higher BTU. If your climate regularly exceeds 90 degrees Fahrenheit, you should increase your BTUs by about 30%.

Air Conditioner In Hot Climate

Other Room Factors
  • Window and Doors
    The number of windows and doors in your room will impact how well insulated it is. You’ll need a more powerful AC system with higher BTUs to counteract this. This will also impact the placement of the system, and you’ll need to find a mini split that can fit in the remaining space.
  • Direct Sunlight
    Direct sunlight heats the room a lot. If your room has a lot of sunlight, you’ll need a larger and more powerful AC system to cool it down effectively.
  • Internal sources of heat
    Different appliances like heaters, cookers, or dryers will all give off heat, and your AC system will need to handle it effectively. The more internal sources of heat, the more BTUs you need. Also, bear in mind that lightbulbs can give off heat, too, so you should consider how many lights you have in a room.
  • Number of Occupants
    People generate a large amount of body heat which will make it more difficult to cool a room. Consider how many people can use a room and how often they spend time in there because this will impact the size of the mini split you need.
  • Floor Type
    Carpeted floors offer a great deal more insulation than hardwood floors, so it should be easier to heat or cool a carpeted room. The type of flooring you have will impact the type of mini split you need.

What Size Mini Split AC Do I Need?

Size Of Mini Split Systems

When considering the size of mini split you need, there are two aspects to think about, the outdoor compressor and the indoor units.

No matter how many rooms or zones your AC will be operating in, you are likely to only have one compressor. Most major brands like Mr Cool, Mitsubishi, and Pioneer offer a range of external compressor sizes, but others may have fixed dimensions. The manufacturer should make it clear how many zones or the area that they can support.

You then need to consider the indoor units. For this, there are two steps:

1. Determine the Number of Rooms

Look around your home and determine how many rooms you want a mini split in. Most mini split AC systems can be fitted in 8 or more rooms, but you may not need that much coverage. It’s often best to start by considering what the busiest or most used rooms are and then go from there.

2. Find the dimensions of each room

You’ll need to work out the square footage of each room. Do this by measuring the length and the width of each room and multiplying them together.

E.g. if your room is 30ft long and 40ft wide, then 30×40= 1200 square feet.

3. Get the BTU rating

Finally, you need to get your BTU rating. This can be determined by taking your square footage and multiplying it by 25. So, for a 1200 square foot room, the BTU needed is 30,000. Take this as a range with a leeway of a few thousand BTU on each side.

Once you have the BTU range that you need, you can start to look at the best mini split AC system for you. Remember, sometimes it’s worth getting an expert to check your work at this stage just to make sure you’re on the right track.

Many brands have a specific mini split size guide, so it’s worth looking for their specific measurements.

The BTU Sizing Guide (British Thermal Units)

BTU Defined

A BTU (British Thermal Unit) is a key figure in determining the size of mini split AC you need in your home. In simple terms, it’s a measurement of thermal energy, and it shows you the amount of heat required to warm or cool 1 pound of water by 1 degree Fahrenheit.

By understanding the BTUs needed in your home, you can make an informed decision about the size of mini split required. In general, the bigger the house, the more BTUs are needed, but the factors further up in this article also play a role.

The table below gives a detailed guide for the BTUs needed for different sized homes but remember you can use the equation above to check for yourself.

Area (square foot)BTUs

People Also Ask (FAQ)

What size mini split is suitable for a 1-car garage?

A 1 car garage would typically need a 6000 BTU mini split. This is generally a small, single unit. Of course, this would be impacted by the exact dimensions of the garage.

What size mini split is suitable for a 2-car garage?

A 2-car garage would generally only need a single unit and you want about 9000 BTUs. Again, this is dependent on the exact dimensions of the garage.

How many square feet does a 1-ton mini split cool?

A 1-ton mini split is equivalent to about 12000 BTUs and can cool around 600-650 square feet.

What size breaker for an 18000 BTU mini split AC?

Your breaker should be 15-20A for this sized mini-split.

How many rooms can a single mini split cool?

A single mini split is generally used in a single room or zone, but you can add extra evaporator units, and it will comfortably be able to deal with 4 rooms at once. The effectiveness of the mini split will be impacted by the exact size of each room, though.


Mini split air conditioners are excellent additions to any home. They can be expensive, but when set up correctly, they offer a great deal of value, so it’s essential to get the right size.

Hopefully, this article has given you everything you need to know, and you now have the confidence to find, purchase and install a mini split AC system that’s perfect for your home.

Josh Mitchell

Josh Mitchell

My name is Josh and I am obsessed with DIY and improving my family home. HVAC topics can be tricky for homeowners so I decided to share my knowledge on the subject. When I am not working on DIY projects, you can find me at the beach or my local coffee shop.