Mini Split Size Calculator: Find the Right Ductless BTU & Tonnage for Your Room

Mini Split Sizing Chart by BTU and Room Size

Most people come here with one of two questions. Either they know their room size and want the BTU number, or they already have a unit in mind and want to know what room it will actually handle. So below we have answered it in both directions using the same bands the calculator uses.

The bands come from a baseline of about 20–25 BTU per square foot. A hot and humid climate pushes you to the top of each band, and a cold climate lets you sit at the bottom. If your room lands right on the edge between two sizes, go with the smaller one unless the room has high ceilings, heavy afternoon sun, or more than two people in it regularly.

Mini Split BTU Per Square Foot: The Number We Start From

The working number is 20 to 25 BTU per square foot. So a 400 sq ft room comes out at 8,000 to 10,000 BTU before any adjustments. Then ceiling height, climate, sun, insulation and the number of people push that up or down, and the last step is snapping the result up to a size that mini splits are actually sold in. That last step matters more than people expect, because you cannot buy a 10,000 BTU ductless head. You buy 9,000 or you buy 12,000.

6000 BTU Mini Split Room Size and Why It Is Hard to Find

A 6,000 BTU mini split suits a room under 150 sq ft. This is the smallest ductless head sold, and it is not on our calculator's size ladder because most brands start at 9,000. Only a few manufacturers make a 6,000 head. If your room is this small, read the small room section below before you buy anything, because the honest answer is not always a mini split.

9000 BTU Mini Split Square Footage: What It Really Covers

A 9,000 BTU (0.75 ton) mini split covers roughly 150 to 350 sq ft. That is the standard bedroom, home office, or small studio size. In a hot and humid climate treat 300 sq ft as your ceiling, and in a cold climate you can stretch it closer to 350. It is the most commonly sold head size for a reason, because most bedrooms fall inside this band.

12000 BTU Mini Split Square Footage Explained

A 12,000 BTU (1 ton) mini split covers roughly 350 to 500 sq ft. Large bedrooms, master suites, small living rooms, and most converted garages sit in this band.

This is also the size people most often buy too early. If your room is 300 sq ft and someone tells you to go 12,000 "just to be safe", you are giving up humidity control for capacity you will never use. Basically the unit will hit your temperature quickly and then spend the rest of the afternoon idling instead of pulling moisture out of the air.

12000 BTU Mini Split Room Size in Plain Numbers

Ceiling height is what quietly changes this answer, and it is the reason two people with the same floor area get told different things. A 12,000 BTU head is comfortable in about a 20 ft × 24 ft room while the ceilings are the standard 8 ft. Raise those ceilings to 10 ft and the same head is really only good for around 400 sq ft, because you are cooling a volume of air and not a floor. So if your room has a vaulted or cathedral ceiling, measure the height and put it into the calculator rather than working from the floor plan.

18000 BTU Mini Split Square Footage and the Single Head Limit

An 18,000 BTU (1.5 ton) mini split covers roughly 500 to 750 sq ft. Open plan living and dining areas, large great rooms, and small open floor apartments. This is the largest size that still works well as a single head, because past about 750 sq ft you usually run into a different problem, which is not capacity but air distribution. One head can only throw air so far.

24000 BTU Mini Split Square Footage for Open Floors

A 24,000 BTU (2 ton) mini split covers roughly 750 to 1,000 sq ft. At this size you are usually cooling a whole floor or a large open plan area rather than a room. Before you buy a single 24,000 head for 1,000 sq ft, check whether that space is genuinely open. If there are doors in it, the honest answer is two smaller heads instead of one big one.

36000 BTU Mini Split Square Footage and the 30,000 BTU Step Below It

A 36,000 BTU (3 ton) mini split covers roughly 1,250 to 1,500 sq ft, and a 30,000 BTU (2.5 ton) sits just under it at about 1,000 to 1,250 sq ft. At this point almost nobody is running a single head. These capacities are normally the outdoor unit rating for a multi zone system feeding three or four indoor heads, which is a different sizing job. We have covered that further down.

1 Ton Mini Split Square Footage in Tons and BTU

Where people get stuck here is the labelling, not the number. Ductless brands almost always print BTU on the box, while central and split systems are sold in tons, so the same capacity gets described two different ways depending on which aisle you are standing in. One ton is 12,000 BTU, and a 1 ton mini split covers about 350 to 500 sq ft.

The model number usually tells you before the spec sheet does. Most ductless model numbers carry the capacity in hundreds or thousands of BTU, so a model with 09 in it is a 9,000 BTU head and one with 12 is 12,000. And a warning worth repeating, because it catches people out. A 1 ton mini split and a 1 ton central AC are the same amount of cooling, but they are not interchangeable equipment. One serves a single room through a wall head, the other serves a whole house through ducts, so the same tonnage does a completely different job. If you need to move between the two units for any size, our BTU to ton conversion chart lists every common step.

2 Ton Mini Split Square Footage: The Biggest Single Head

Two tons is 24,000 BTU, and it is worth understanding why this is the point where installers stop adding capacity and start adding heads instead. It is not that bigger indoor units do not exist. It is that a wall head is a fan blowing into a room, and past roughly 750 to 1,000 sq ft the limit stops being how much heat it can remove and becomes how far it can throw the air.

So what happens when someone does put one 2 ton head on a 1,000 sq ft floor with doors on it? The room the unit is in gets cold, the far bedrooms stay warm, and the unit reaches its setpoint early because the thermostat is in the room that is already cooled. You end up with capacity you paid for that never reaches the rooms that needed it. Above 2 tons, the right question changes from what size do I need to how many heads do I need, which is a different job and we have covered it below.

How to Size a Mini Split for Your Room Size

Below are the room sizes people ask about most. Each one assumes standard 8 ft ceilings, average insulation, and a couple of people in the room. If your situation is different from that, put your actual numbers into the calculator above, because these are starting points and not a substitute for your own room details.

Mini Split for 100 Sq Ft: Why Nothing Is Small Enough

A 100 sq ft room needs somewhere around 2,000 to 2,500 BTU, and that is the problem. Nothing that small is sold. The smallest ductless head on the market is 6,000 BTU and most brands start at 9,000, so even the smallest unit you can buy is two to four times bigger than the room needs. Read the small room section below before spending money here.

Mini Split for 150 Sq Ft Rooms

At 150 sq ft you are at the bottom edge of the 9,000 BTU band, and a 9,000 head will work here. It will run at low output most of the time, which is fine on an inverter unit. If you can find a 6,000 BTU head instead, that is the better buy, because it will run longer at a lower speed and pull more moisture out of the air while it does.

Climate decides how much the oversizing costs you. One owner put a 12,000 BTU unit into a 120 sq ft studio in temperate northern California, which on paper is badly oversized, and reported it working perfectly. That works because the air there is dry, so there is very little moisture for the unit to fail to remove. Try the same thing in Florida or the Gulf coast and you get a cold, clammy room instead.

Mini Split for 200 Sq Ft Bedroom

A 200 sq ft room wants a 9,000 BTU mini split. This is a normal bedroom, so it is the most common answer on this whole page. Do not size up to 12,000 because the room gets afternoon sun. Select high sun exposure in the calculator instead and see what it actually does to the number, which is usually about 10 percent, not 30.

One thing to expect at this size, and it matters more in a bedroom than anywhere else. An owner running a 9,000 head in a 180 sq ft insulated shed found it heated fine down into single digit temperatures, but the temperature swung about 4°F either side of the set point. Their words were that it is fine for a shed and would bother them greatly in a bedroom. So if you are sizing a room you sleep in, the unit's minimum output matters as much as its maximum.

What Size Mini Split for 250 Sq Ft Room

250 sq ft is comfortably inside the 9,000 BTU band. A 9,000 head handles it in every climate zone we cover. The only reason to go to 12,000 here is if the room is a kitchen, because appliance heat adds a flat load on top of the floor area that square footage alone never captures.

What Size Mini Split for 300 Sq Ft Room

300 sq ft still lands on 9,000 BTU in most climates, and pushes to 12,000 in hot and humid zones. This is the first size where the climate zone genuinely changes the answer, so it is worth picking your zone properly in the calculator rather than guessing.

Glass changes it more than climate does. A 16 ft × 16 ft four season room, which is 256 sq ft, came up on a heat pump forum with the owner considering a 1 ton unit. The response from people who size these for a living was that 1 ton would be overkill even for a glass room on Long Island, and that an insulated apartment in Anchorage might need 6,000 BTU while a badly designed Florida sun room might need 18,000 at the same floor area. So at this size the walls tell you more than the square footage does.

Mini Split for 400 Sq Ft Room or Studio

A 400 sq ft room needs a 12,000 BTU mini split. Converted garages, large master bedrooms, and studio apartments usually land right here. If it is an actual garage with an uninsulated door, the answer changes, and we have covered that separately below because a garage is not just a room with a car in it.

The old rule of thumb people quote is that one ton covers about 440 sq ft, which is why 400 sq ft sits comfortably on a 12,000 BTU head. Where that rule breaks is on a poor envelope. Someone sizing a 400 sq ft two car garage in South Florida was told by most people to take the 18,000 rather than the 12,000, not because the floor area demanded it but because an uninsulated garage door and an attic above it add load that the square footage never shows. Same 400 sq ft, one size difference, and the envelope is what decided it.

What Size Mini Split for 500 Sq Ft: The Line Between Two Sizes

500 sq ft sits right on the line between 12,000 and 18,000 BTU. In a temperate or cold zone, 12,000 is enough. In a hot and humid zone, or if the space has vaulted ceilings, go to 18,000. This is the single most argued about size in this whole category and the honest answer is that the climate zone decides it, not the square footage.

What Size Mini Split for 600 Sq Ft Open Space

600 sq ft needs an 18,000 BTU mini split. At this size, start thinking about the shape of the space and not only its area. 600 sq ft in one open rectangle is an easy job for one head. The same 600 sq ft split into a living room and two bedrooms is not, no matter what size unit you buy.

The envelope can move this number a long way in the other direction too. One owner in New Hampshire runs a 24 ft × 24 ft room, which is 576 sq ft, on a single 9,000 BTU unit with double pane windows and 2x4 wall insulation. That is half the size our band suggests, and they deliberately undersized it because the extreme days are rare where they are. So treat 18,000 as the safe answer for average construction, and know that a well insulated room in a mild climate can need much less.

What Size Mini Split for 700 Sq Ft and the Single Head Limit

700 sq ft calls for an 18,000 BTU mini split, and it is close to the practical limit for a single indoor head. You will get the capacity you need, but expect the far corners of the room to sit a few degrees off the temperature near the unit. A ceiling fan fixes most of that for a lot less money than a second head.

Here is the thing that surprises people at this size. Manufacturer square footage ratings are written conservatively, so the number on the box is not the number you are stuck with. A 9,000 BTU head rated by its maker for around 400 sq ft has been reported running a 750 sq ft great room in a hot desert climate with insulation the owner described as not great, mainly because the room faces north and never takes direct sun. So orientation and shading can matter as much as floor area, which is exactly why we ask about sun exposure in the calculator rather than sizing on square footage alone.

What Size Mini Split for 800 Sq Ft Depends on the Layout

800 sq ft needs 24,000 BTU on paper. But here is the thing some people miss at this size. Whether one head can serve 800 sq ft depends almost entirely on whether it is open plan. If it is one great room, a single 24,000 head is fine. If it is a floor with doors on it, you want two heads on a multi zone system instead, and the total BTU across those two heads will be lower than 24,000, not higher.

If the unit is also your heat, this is where the cooling number stops being the number that matters. An owner in Massachusetts running a 12,000 BTU unit over 800 sq ft found it heated the space until the outside temperature dropped to about 30°F, and after that it spent too much of its time defrosting to keep up, because it was a basic model rated only to around 19°F. On the cooling side, another installer put it plainly that 15,000 BTU is too small for 800 sq ft with two people in it unless the insulation is very good. So 24,000 is the honest cooling answer, and if you are heating with it as well, read the cold climate section further down before you choose a model.

What Size Mini Split for 900 Sq Ft First Floor

900 sq ft points to 24,000 BTU. Same warning as above, only stronger. A 900 sq ft first floor divided into four rooms is not a one head job, and if an installer quotes you a single 12,000 head for a space like that, ask them to show you the load calculation before you sign anything.

That example is not hypothetical. A homeowner in Maine was quoted exactly that, one 12,000 BTU head for a 900 sq ft first floor split into four rooms, and the salesperson admitted up front there would be roughly a 10°F difference from one end of the floor to the other. The responses from installers were consistent, that one head does not serve four rooms, and that a rough working limit is about 500 sq ft per head unless the space is genuinely open. Capacity was never the problem in that quote. Air distribution was.

What Size Mini Split for 1000 Sq Ft Home or Open Space

1,000 sq ft needs about 24,000 BTU in a moderate climate and 30,000 BTU in a hot one. For an open 1,000 sq ft space, one 24,000 head can do it. For a normal 1,000 sq ft home with bedrooms, the right design is a multi zone system with two or three smaller heads sized per room, which we have explained below.

Open plan is doing the heavy lifting in that first answer. An owner of a 960 sq ft lake house in Pennsylvania with a high ceilinged great room reported a single 18,000 BTU unit handling the whole house, which they had not expected, in a building they described as getting as cold as a movie theater and as hot as a sauna. Their own advice afterwards was that they would go smaller than 18,000 next time. So for a genuinely open 1,000 sq ft, the number our calculator gives you is the safe one rather than the minimum.

What Size Mini Split for 1200 Sq Ft: Time to Think in Zones

1,200 sq ft works out to roughly 30,000 BTU total. At this size you are no longer buying a mini split, you are designing a system. That total gets split across two to four indoor heads, and each head is sized from the room it serves rather than from the house total divided evenly.

What Size Mini Split for 1500 Sq Ft House

1,500 sq ft comes out around 36,000 BTU total, normally as a three or four zone system. Do not let anyone sell you a single 36,000 head for a 1,500 sq ft house. It will cool the room it is in and do very little for the rest, and you will have paid for capacity that never reaches the rooms that needed it.

Mini Split for 2000 Sq Ft: A Whole House Job

2,000 sq ft lands near 48,000 BTU total, which is the top of the ductless ladder, and it is genuinely a whole house job. Four or five zones is normal here. At this point it is worth pricing a ducted system against the ductless one, because once you are running five heads the cost advantage of going ductless has mostly disappeared. Our HVAC load calculator gives you the whole house number to compare against.

It does not always take five heads though, and this is where an open floor plan pays you back. One owner replaced a failed central system in a 2,000 sq ft home with just two 18,000 BTU units, so 36,000 BTU in total rather than 48,000, and reported the power bill dropping by about half afterwards. That works when the layout lets air move between the areas each head serves. In a 2,000 sq ft house chopped into eight rooms, it would not.

Multi Zone Mini Split Sizing

A multi zone system is one outdoor unit running two or more indoor heads. It sounds like the obvious choice when you have several rooms, and often it is. But there is one thing about how these systems behave that almost nobody explains before you buy, and it changes which setup you should pick.

Every multi zone outdoor unit has a minimum output as well as a maximum. Let me tell you what that means in practice. Say your outdoor unit will not run below 10,000 BTU, and one night only your 7,500 BTU bedroom head is calling for cooling. The compressor still has to produce its minimum. That extra capacity does not disappear, it gets pushed into the refrigerant lines and coils of the heads that are switched off.

In cooling this is mostly wasted energy. In heating it is worse, because the expansion valves on the idle heads have to stay partly open to stop liquid refrigerant stacking up in them, so those idle heads sit there quietly getting warm. Owners of five head systems have measured this at roughly 200 watts of heat per idle head. So the rooms you are not heating get heated anyway, a little.

There is one more thing worth knowing. The SEER2 number printed on a multi zone box is measured with every head running. Basically that is the best case, not your normal Tuesday. A single zone unit of the same rating will usually beat it in real use, because it was tested doing the job it actually does. If you want to see what a rating difference is actually worth in money before you pay extra for it, our SEER energy savings calculator works that out by climate and runtime.

So the practical rule is this. Do not put every room on one big outdoor unit just because you can. Two dual zone systems will usually run better than one four zone system, because each one can turn down further, and if one fails you still have half your house working. The trade off is more outdoor units, more wall penetrations, and more breaker slots.

2 Zone Mini Split: The Easiest One to Get Right

A 2 zone mini split is the easiest multi zone system to get right, and usually the one we would suggest first. Two heads, one outdoor unit, and a turndown range that still works when only one room is calling. Typical outdoor sizes are 18,000 or 24,000 BTU feeding two 9,000 or 12,000 heads. Size each head from its own room, then check the outdoor unit covers the total.

3 Zone Mini Split for a Small House or One Floor

A 3 zone mini split normally means a 24,000 to 36,000 BTU outdoor unit feeding three heads, and it suits a small house or one floor with a living area and two bedrooms. This is about where the minimum output problem starts to show. If two of your three rooms are small bedrooms that rarely run at the same time, the system will spend a lot of its life above the load you actually have.

4 Zone Mini Split and When to Split It in Two

A 4 zone mini split usually runs from a 36,000 or 48,000 BTU outdoor unit. It covers a lot of house from one condenser, and it only needs one set of outdoor plumbing and one pair of breaker slots instead of four. But it is also where we would stop and ask whether two dual zone systems would serve you better. Also check the manufacturer's head count limit before you plan it, because some outdoor units are rated for a maximum number of heads regardless of the total BTU.

5 Zone Mini Split for Whole House Heating and Cooling

A 5 zone mini split is a whole house system, normally on a 48,000 BTU outdoor unit. Everything above applies more strongly here. Five heads on one compressor means the gap between your smallest realistic load and the unit's minimum output is at its widest. If you are planning five zones, it is worth pricing a ducted system alongside it, because at that point the install cost of ductless has usually caught up with ducted anyway.

Cost follows head count more than it follows capacity, which is the part that surprises people. Adding a zone means another indoor unit, another line set, another wall penetration and more labour, so a four zone job is not twice the price of a two zone one. Work out how many heads you actually need first, then price it with our HVAC replacement cost calculator, which prices single zone and multi zone ductless separately.

Mini Split for a Small Room Under 150 Sq Ft

This one deserves its own section because the usual advice does not work here. For a room under 150 sq ft, the problem is not calculating the size. The problem is that nobody makes a unit small enough.

A 100 sq ft room needs somewhere around 2,000 to 2,500 BTU. The smallest ductless head sold is 6,000 BTU and most brands start at 9,000. So the smallest thing you can buy is already two to four times the load. And that is where people run into trouble. We have seen owners with a 9,000 head in a 100 sq ft room report that it can never hold the temperature or the humidity properly, because it reaches the set point almost immediately and then stops doing useful work.

So what actually decides whether it works is not the unit's capacity. It is the unit's minimum output, sometimes called turndown. That number is not on the front of the box, but it is the one that matters in a small room.

The spread is large. Some 6,000 BTU single zone units modulate all the way down to roughly 1,000 BTU per hour while drawing about 100 watts. At that point even a slightly oversized unit costs you very little, because it is barely working. A larger head might not go below 5,000 to 8,000 BTU, which in a 100 sq ft room means it is either overshooting or switching off. So when you compare two units for a small room, look up the minimum capacity, not just the nominal size.

And here is the answer most sites will not give you. For a genuinely small room, a modern inverter window unit is often the better buy. It costs a fraction of a ductless install, the small sizes actually exist, and there are models made for horizontally sliding windows now. If you want to size one properly, use our window AC BTU calculator. A mini split is a great piece of equipment, but it is not automatically the right answer for a 100 sq ft office.

One Head or Several? Why Layout Beats Square Footage

If we simply look at it, a bigger space needs more BTU, and that is true. But square footage alone will mislead you here more than with any other type of AC, because a ductless head has no ducts to carry the air for it. It blows into the room it is mounted in and that is all it does.

So the practical limit for one head is around 500 sq ft of genuinely open space. It can serve more than that when the area is one open rectangle, and much less when there are doors and corners in the way. A 900 sq ft first floor divided into four rooms is not a one head job even though the BTU math says a single unit could cover the load. The capacity is there, the air just never arrives.

The symptom to expect when you push this too far is a temperature gradient. Owners regularly report 10°F between the room with the head in it and the far end of the floor. Installers will often tell you this up front, and it is worth listening when they do. If a space has doors that get closed, plan a head for each of those rooms, or accept that those rooms will not be conditioned.

There are cheaper fixes worth trying before adding a second head. A ceiling fan or a small fan pointed at the ceiling breaks up the warm layer that collects there, and in a room that already has ductwork but poor airflow, an inline duct booster costs about a hundred dollars against several thousand for another zone.

Sizing a Mini Split for a Garage, Sunroom, or Server Room

Some spaces do not behave like rooms. In these cases the square footage is the least useful number you have, so it is worth treating them separately instead of running them through a normal room calculation.

Mini Split for Garage: Insulate First, Size Second

A garage is not just a room with a car in it. The door is usually a large uninsulated panel, the walls are often unfinished, and the ceiling may be open to an unconditioned attic. So the same 400 sq ft that needs 12,000 BTU inside your house can need 18,000 BTU as a garage.

The advice worth following before you buy anything is to insulate first, size second. Foam board panels in the door sections and seals around the top and sides are cheap, and they cut the load enough to change which unit you need. If you insulate the door and ceiling of a two car garage, a 12,000 head often becomes viable where an 18,000 was needed before.

Ductless Mini Splits for Sunrooms and Four Season Rooms

A sunroom or four season room is a glass box, and glass has almost no insulating value. So the load here is driven by the window area and which direction it faces, not by the floor area. A 16 ft × 16 ft sunroom with glass on three sides facing south and west is a genuinely hard space to condition, and it can need double what the same footprint would need as an ordinary room. It is also the space most likely to leave you with a humidity problem, because the load swings so hard between a sunny afternoon and an overcast one.

Mini Split for a Server Room or Network Closet

Here the floor area barely matters at all. What matters is how many watts of equipment you have running in there, because essentially all of it turns into heat. The conversion is simple: watts × 3.41 = BTU per hour. So 3,000 watts of gear is about 10,200 BTU before you count the room itself.

Two things are different about these rooms. The load is almost entirely sensible heat with very little moisture, so dehumidification is not the concern it is elsewhere, and oversizing is far less risky than in a bedroom. And redundancy matters more than efficiency. Two smaller units mean you can service one without shutting the room down, which is why you often see a pair of units in a space that one could technically handle. Getting enough air across the racks matters just as much as the capacity, so our HVAC CFM calculator is worth a look for the airflow side.

Mini Split in an RV or Tiny Home

People do fit ductless heads to RVs, toy haulers and tiny homes, and the sizing rules change completely because the envelope is so thin. Walls that are 2 inches instead of 4 to 6 give you far more heat gain for the same floor area, and in desert sun a dark roof can run 30 to 50°F hotter than a white one. So a 400 sq ft RV can need the size you would normally put in a room twice as big. If that is your situation, our RV air conditioner size calculator uses an envelope model built for exactly that, rather than the room based math on this page.

Cold Climate Mini Split Sizing

If you are only cooling, you can skip this. But if the mini split is also your heat, the sizing job changes, because your heating load and your cooling load are usually not the same number.

In a cold climate the heating load is normally the larger of the two, sometimes by a lot. A well sealed 400 sq ft space might need 10,000 BTU of cooling in July and 24,000 BTU of heating in January. When the two numbers differ, size for the larger one, which in a cold climate means sizing for heat. An inverter unit will simply idle down during the cooling season, and running at 25 percent of capacity is something these units do well.

But there is a real trade off and you should know about it. Mini splits are not strong at removing moisture at the best of times, and at very low output that ability drops off further. So if you size for heating in a humid region, expect to run the unit in dry mode during shoulder seasons, or pair it with a separate dehumidifier sized for the space.

One more thing that catches people out. A standard unit rated down to about 19°F does not simply stop at 19°F, it fades before that. In damp cold around 30°F it starts spending more of its time defrosting and less of it heating, so the output you actually get is below what the label suggests. A hyper heat or cold climate model holds its capacity much further down. So check the rated heating output at your design temperature rather than the nominal BTU on the box. If heating is the main job, our heat pump size calculator sizes for both loads together.