What Size Mini Split Do I Need? A Sizing Chart by Square Feet
To answer "what size mini split do I need," start with the ENERGY STAR sizing chart. A 500 sq ft room needs about 12,000 BTU. A 1,000 sq ft open space needs about 18,000 to 21,000 BTU, which points to a 24K. Add more for strong sun, a kitchen, tall ceilings, poor insulation or cold winters.
Want a number for your exact room? Try our mini split sizing calculator. Sizing a whole home? Use our Manual J calculator.
BTU stands for British thermal unit. It measures how much heat a unit can move in one hour. A higher BTU number means more heating and cooling power.
Jump to:
- Sizing chart by square feet
- MRCOOL DIY size table
- How to size a mini split in 4 steps
- 500 sq ft
- 1,000 sq ft and whole homes
- Oversize or undersize?
- Heating or cooling?
- FAQ
What size mini split do I need for my square footage?
ENERGY STAR has a simple chart that matches room size to cooling power. Find your room size on the left. Then read the BTU number on the right.
| Room size (sq ft) | Cooling power needed (BTU per hour) |
|---|---|
| 100 up to 150 | 5,000 |
| 150 up to 250 | 6,000 |
| 250 up to 300 | 7,000 |
| 300 up to 350 | 8,000 |
| 350 up to 400 | 9,000 |
| 400 up to 450 | 10,000 |
| 450 up to 550 | 12,000 |
| 550 up to 700 | 14,000 |
| 700 up to 1,000 | 18,000 |
| 1,000 up to 1,200 | 21,000 |
| 1,200 up to 1,400 | 23,000 |
| 1,400 up to 1,500 | 24,000 |
| 1,500 up to 2,000 | 30,000 |
| 2,000 up to 2,500 | 34,000 |
Source: ENERGY STAR, Room Air Conditioners.
Keep two things in mind. ENERGY STAR wrote this chart for room air conditioners, not mini splits. It also assumes an 8 ft ceiling. Use it as a starting point for one room. Then adjust it for your space.
Which MRCOOL DIY size fits my room?
MRCOOL lists how many square feet each DIY size can cover. Here are those numbers for the systems we sell.
| Size | Listed coverage (up to) | 5th Gen system | Easy Pro system |
|---|---|---|---|
| 9K (9,000 BTU) | 400 sq ft | 9K 5th Gen | 9K Easy Pro |
| 12K (12,000 BTU) | 550 sq ft | 12K 5th Gen | 12K Easy Pro |
| 18K (18,000 BTU) | 800 sq ft | 18K 5th Gen | 18K Easy Pro |
| 24K (24,000 BTU) | 1,050 sq ft | 24K 5th Gen | 24K Easy Pro |
| 36K (36,000 BTU) | 1,550 sq ft | 36K 5th Gen | No 36K Easy Pro |
Source: MRCOOL DIY 5th Gen brochure and Chill Mini Splits product listings.
These are MRCOOL's "up to" numbers, based on ideal install conditions. Real rooms often need more power, so use the adjustments below before you pick. See every size in our MRCOOL DIY 5th Gen single-zone systems and MRCOOL DIY Easy Pro collections.
How do I size a mini split in 4 steps?
- Measure the room in square feet.
- Find the BTU number in the ENERGY STAR chart.
- Add or subtract for sun, shade, people, kitchens, ceilings and insulation.
- Match the result to the MRCOOL size table above.
How do I measure my room in square feet?
Multiply the length of the room by its width. A room that is 20 ft long and 25 ft wide is 500 sq ft. Turn inches into part of a foot, so 6 inches is 0.5 ft.
ENERGY STAR says to split odd shapes into squares, rectangles and triangles. Find the area of each part, then add them up. For a triangle, multiply length by width and divide by two.
How much should I add for sun, kitchens and people?
ENERGY STAR gives four simple adjustments:
- Very sunny room: add 10%.
- Heavily shaded room: take off 10%.
- More than two people in the room most of the time: add 600 BTU for each extra person.
- Kitchen: add 4,000 BTU for the heat from cooking.
How do tall ceilings change the size?
The ENERGY STAR chart assumes an 8 ft ceiling. Taller ceilings mean more air to cool. ENERGY STAR does not give a set amount to add. Our calculator's rule of thumb is to add about 10% for each extra foot of height. A 10 ft ceiling is 2 extra feet, so add about 20%.
How do insulation and climate change the size?
Our calculator's rule of thumb is to add 10% to 20% for poor insulation. That covers spaces like sunrooms and older homes. Garages and workshops often have little insulation, so use our garage and workshop sizing guide for those spaces.
Climate matters too. Hot climates, cold climates and drafty homes need more power than the chart shows. The U.S. Department of Energy (DOE) gives no simple percentage for this. It points to a load calculation called Manual J. Manual J is the standard method HVAC pros use to find how much heat a home gains and loses. Our Manual J calculator asks about your climate, insulation, windows and ceilings.
What size mini split do I need for 500 sq ft?
A typical 500 sq ft room needs a 12,000 BTU mini split. ENERGY STAR lists 12,000 BTU for rooms from 450 up to 550 sq ft. The MRCOOL DIY 12K 5th Gen lists coverage up to 550 sq ft, so a 500 sq ft room fits its range.
Real rooms can change the math. Here are three 500 sq ft rooms with the ENERGY STAR adjustments:
| 500 sq ft room | Math | BTU needed | Closest MRCOOL size |
|---|---|---|---|
| Typical room | Chart value | 12,000 | 12K |
| Very sunny room | 12,000 + 10% | 13,200 | 18K |
| Kitchen | 12,000 + 4,000 | 16,000 | 18K |
The sunny room and the kitchen both need more than 12,000 BTU. That points to the 18K 5th Gen or the 18K Easy Pro. Check your own room with our mini split sizing calculator before you buy.
What size mini split do I need for 1,000 sq ft or a whole home?
A 1,000 sq ft space needs about 18,000 to 21,000 BTU. ENERGY STAR lists 18,000 BTU for 700 up to 1,000 sq ft and 21,000 BTU for 1,000 up to 1,200 sq ft. The MRCOOL DIY 24K 5th Gen system lists coverage up to 1,050 sq ft. That makes the 24K the closest match for one open 1,000 sq ft space. One indoor unit cannot push air into rooms behind closed doors, though.
Should I use one big unit or several smaller ones?
One big unit rarely keeps every room comfortable. A multi-zone system uses one outdoor unit with two or more indoor units. Each room gets its own indoor unit and its own temperature setting. One example is the MRCOOL DIY 2-zone 18K (9K + 9K). It runs two indoor units from one outdoor unit. A 9K + 12K version is also available. You can also put a separate single-zone system in each room. Our guide on multi-zone vs multiple single-zone mini splits compares both. To pick the right sizes, read how to size a MRCOOL multi-zone system.
When should I use the Manual J calculator?
Use the Manual J calculator for a whole home. It is also the better tool for a main heat source or a very hot or cold climate. It looks at the whole house, not just one room.
Is it better to oversize or undersize a mini split?
Neither is good. Aim for the size that fits the room. Bigger is not safer.
An oversized unit cools the room fast, shuts off, then turns back on. This on and off pattern is called short cycling. ENERGY STAR says a unit that is too big cools the room before it can remove the humidity. That leaves the air cool but damp and clammy. The DOE adds that a unit that is far too big cycles more and runs less efficiently. ENERGY STAR's HVAC quality installation guidance also warns that frequent cycling can shorten equipment life.
An undersized unit has the opposite problem. It runs nonstop on the hottest and coldest days and may still not keep up.
Mini splits like the MRCOOL DIY 5th Gen use DC inverter compressors. An inverter can slow down instead of shutting off, which helps with a little extra size. But every inverter has a lowest speed. A unit that is much too big will still cycle on mild days.
Not sure which size is right? Call our team at 888-231-8920 for a free sizing check.
Do I size a mini split for heating or cooling?
Size for both. The ENERGY STAR chart only covers cooling. A heat pump mini split also heats your home. On the coldest days, its heat output can be lower than the number on the label.
Some homes use a heat pump as the main heat in a cool or cold climate. The DOE says those homes should use cold-climate sizing methods. That covers IECC climate zone 4 and colder. IECC is the climate map used in U.S. building codes. Check how much heat the unit puts out at your usual winter low. Our cold-climate guide explains how to do that.
What else do I need once I pick a size?
- Line set: This is the copper tubing that links the indoor and outdoor units. Learn how to measure line-set length, then shop mini split line sets.
- Power: The 9K and 12K systems in our table run on 115V, and the 18K and larger need 230V. Read 115V vs 230V before you buy.
Frequently asked questions
How many square feet does a 12,000 BTU mini split cool?
A 12,000 BTU mini split cools about 450 to 550 sq ft. That is the ENERGY STAR range for 12,000 BTU. The MRCOOL DIY 12K lists coverage up to 550 sq ft under ideal conditions.
What size mini split do I need for 1,000 sq ft?
You need about 18,000 to 21,000 BTU, based on the ENERGY STAR chart. For one open space, the MRCOOL DIY 24K is the closest match. It lists coverage up to 1,050 sq ft. Homes with separate rooms do better with a multi-zone system or several single-zone units.
Is it better to oversize or undersize a mini split?
It is better to match the size to the room. An oversized unit short cycles and can leave the air damp. An undersized unit runs nonstop and may not keep up on very hot or cold days.
How much should I add for a kitchen or a sunny room?
ENERGY STAR says to add 4,000 BTU for a kitchen and 10% for a very sunny room. A 500 sq ft kitchen needs about 16,000 BTU. A very sunny 500 sq ft room needs about 13,200 BTU.
Do I size a mini split for heating or cooling?
Size for both. Use the chart to check the cooling need. Then make sure the unit puts out enough heat at your usual winter low. This matters most in cold climates and when the mini split is your main heat.
Can one mini split cool a whole house?
One mini split can cool one open space. It cannot push air into rooms behind closed doors. Most homes do better with a multi-zone system or one single-zone unit per room.
Do I need a Manual J calculation for a DIY mini split?
For a single room, the ENERGY STAR chart and our sizing calculator are a good start. Manual J is the better choice for a whole home, a main heat source or a very hot or cold climate. ENERGY STAR and the DOE both point to Manual J. Our free Manual J calculator gives you an estimate.
Sources
- ENERGY STAR, Room Air Conditioners (sizing chart and adjustments): https://www.energystar.gov/products/room_air_conditioners
- ENERGY STAR, Ductless Heating and Cooling: https://www.energystar.gov/products/ductless_heating_cooling
- ENERGY STAR, HVAC Quality Installation: https://www.energystar.gov/saveathome/heating-cooling/hvac-quality-installation
- U.S. DOE Building Science Education, Proper Sizing of HVAC Systems: https://bsesc.energy.gov/energy-basics/hvac-proper-sizing-hvac-systems
- U.S. DOE Building America Solution Center, Ductless (Mini-Split) Heat Pumps: https://basc.pnnl.gov/resource-guides/ductless-mini-split-heat-pumps
- U.S. DOE, Guide to Sizing and Selecting Air-Source Heat Pumps in Cold Climates: https://bsesc.energy.gov/sites/default/files/2024-10/Guide%20To%20Sizing%20%26%20Selecting%20Air-Source.pdf
- ACCA Manual J: https://www.acca.org/standards/technical-manuals/manual-j
- MRCOOL DIY 5th Gen brochure (coverage figures): https://doxrepo.mrcool.com/mc-diy-5-br-en-01.pdf
- Chill Mini Splits Mini Split Sizing Calculator (our in-house rules of thumb for ceilings and insulation): https://chillminisplits.com/pages/mini-split-sizing-calculator
