What Size Mini Split Do I Need? BTU Sizing Chart
A mini split that is the wrong size costs you either way. Too small, and it runs constantly without keeping up. Too large, and it cools the room fast but leaves it clammy, cycles on and off, and wears out sooner.
TheRemodelers works with licensed HVAC contractors to help homeowners get sizing right before they buy. This guide gives you a sizing chart, a step-by-step worksheet, typical sizes for the rooms people most often ask about, and the mistakes contractors see most. For how mini splits compare with other systems, see our complete guide to home HVAC systems.
The Quick Answer
For cooling, a good starting point is about 20 BTUs per square foot of the room. A 500-square-foot room typically needs about 12,000 BTUs, which is a 1-ton mini split. Then adjust for sun, occupancy, and whether the room is a kitchen, using the worksheet below.
Mini Split Sizing Chart by Square Footage
This chart uses ENERGY STAR’s cooling capacity guidance for a room with standard 8-foot ceilings. The last column shows the standard mini split size most installers would choose for that room.
Room Size (sq ft) | Cooling Needed (BTU/hr) | Common Mini Split Size |
|---|
100 – 150 | 5,000 | 6,000 BTU |
150 – 250 | 6,000 | 6,000 – 9,000 BTU |
250 – 300 | 7,000 | 9,000 BTU |
300 – 350 | 8,000 | 9,000 BTU |
350 – 400 | 9,000 | 9,000 BTU |
400 – 450 | 10,000 | 12,000 BTU |
450 – 550 | 12,000 | 12,000 BTU (1 ton) |
550 – 700 | 14,000 | 15,000 – 18,000 BTU |
700 – 1,000 | 18,000 | 18,000 BTU (1.5 tons) |
Mini splits come in fixed sizes, and their inverter compressors can slow down to match a smaller load, so installers usually pick the nearest standard size at or just above the chart number. Above 1,000 square feet, most homes are better served by more than one indoor unit rather than one very large head.
Size Your Room: A Step-by-Step Worksheet
Work through these steps for each room that will get its own indoor unit. The right-hand column follows one example: a sunny 20-by-20-foot living room used by three people.
Step | What to Do | Example |
|---|
1. Measure | Multiply the room’s length by its width to get square feet. | 20 × 20 = 400 sq ft |
2. Base BTUs | Find your square footage in the chart above and note the cooling needed. | 400 sq ft = 10,000 BTU |
3. Sun | Heavily shaded: subtract 10%. Very sunny: add 10%. Otherwise, no change. | Very sunny: +1,000 = 11,000 BTU |
4. People | If more than two people regularly use the room, add 600 BTUs for each additional person. | 3 people: +600 = 11,600 BTU |
5. Kitchen | If you cook in the room, add 4,000 BTUs. | Not a kitchen: 11,600 BTU |
6. Round up | Choose the nearest standard size at or above your total: 6,000, 9,000, 12,000, 15,000, 18,000, or 24,000 BTU. | 12,000 BTU (1 ton) |
7. Check the flags | If any flag in the next section applies, ask a contractor for a load calculation before you buy. | Standard ceilings, good insulation: no flags |
Flags That Mean You Need a Professional Load Calculation
The worksheet assumes a typical room. A contractor should run a Manual J load calculation, which accounts for insulation, windows, orientation, and climate, if any of these apply:
Ceilings taller than 8 feet
Poor or unknown insulation, or a lot of glass
A sunroom, bonus room over a garage, or other room exposed on several sides
You will rely on the mini split for heat in a cold climate
You are sizing a whole home or several rooms at once
12,000 vs. 18,000 vs. 24,000 BTU: Which Do You Need?
Mini split capacity is listed in BTUs or tons. One ton of cooling equals 12,000 BTUs per hour.
Size | Tons | Typical Coverage (Cooling) | Typical Use |
|---|
9,000 BTU | 0.75 | 350 – 400 sq ft | Bedroom or home office |
12,000 BTU | 1 | 450 – 550 sq ft | Living room or large bedroom |
18,000 BTU | 1.5 | 700 – 1,000 sq ft | Open living area or small apartment |
24,000 BTU | 2 | Over 1,000 sq ft | Large open space, though two zones often work better |
Typical Sizes by Room Type
Most sizing questions are about a specific room. These are typical starting points from the chart and adjustments, along with the mistake contractors see most for each.
Bedroom
Most bedrooms of 120 to 250 square feet need 6,000 to 9,000 BTUs. The common mistake is oversizing. An oversized unit in a bedroom cycles on and off and leaves the air damp, which is exactly what you notice at night.
Home Office
A 100- to 150-square-foot office starts at about 6,000 BTUs. Computers, monitors, and printers add heat, so size toward the upper end of the range if the room is full of equipment.
Living Room
A 300- to 450-square-foot living room typically needs 9,000 to 12,000 BTUs. Living rooms often hold more than two people, so remember to add 600 BTUs for each regular occupant beyond two.
Open Kitchen and Living Area
A 500- to 700-square-foot open plan usually lands between 12,000 and 18,000 BTUs once you add 4,000 for the kitchen. People often forget the kitchen adjustment because the space feels like one big living room.
Sunroom
Sunrooms are the room most often undersized. Walls of glass gain far more heat than the chart assumes, and lose more in winter. Treat the chart as a minimum and get a load calculation.
Bonus Room Over a Garage
A room with an unconditioned garage below and a roof above is exposed on several sides, so it usually needs more capacity than its square footage suggests. This is another room where a load calculation pays off.
Basement
Basements sit partly below ground, where the earth keeps them cooler, so they often need less cooling than the chart suggests. The usual mistake here is oversizing, which leaves a basement cool but damp.
Garage or Workshop
Garages are often poorly insulated and have large doors, so the chart, which assumes an insulated room, can badly undersize them. Size from a load calculation, and consider improving insulation first.
Common Sizing Mistakes Contractors See
One big head for a whole floor. Air from a single wall unit doesn’t reach rooms behind closed doors. Several smaller heads on a multi-zone system usually work better.
Copying the old window unit’s size. If the old unit was the wrong size, you repeat the mistake.
Making every head the same size. Each indoor unit should match its own room, even on a shared outdoor unit.
Oversizing “to be safe.” A unit far too large short-cycles and leaves rooms damp.
Ignoring heating. In colder climates, the heating need can exceed the cooling need for the same room.
Treating sunrooms and bonus rooms like ordinary rooms. Their exposure makes the chart unreliable.
Heating Can Change the Answer
The chart and worksheet are for cooling. Most mini splits are heat pumps that also heat, and in colder climates the heating need can be larger than the cooling need for the same room.
If you will rely on a mini split for winter heat, ask for the unit’s heating capacity at your area’s low temperatures, not just its nominal size. Cold-climate models keep more of their heating output in freezing weather. Our guide to heat pump installation cost explains cold-climate performance in more detail.
Sizing a Multi-Zone System
In a multi-zone system, one outdoor unit serves several indoor heads, so sizing happens at two levels:
Size each indoor head for its own room, using the worksheet above.
Add up the indoor heads and choose an outdoor unit within the manufacturer’s matching limits for that combination.
Check that the outdoor unit can deliver enough heating at your winter low temperatures if you will heat with it.
What a Mini Split Costs by System Size
Cost depends mainly on how many indoor units you need. Typical installed prices:
System | Typical Installed Cost |
|---|
Single-zone (one room or open area) | $2,000 – $5,500 |
Dual-zone (two rooms) | $3,500 – $8,000 |
3-zone system | $5,500 – $10,000 |
4-zone system | $8,000 – $15,000 |
Our guide to mini split installation cost breaks down what drives these prices, from line set length to wall mounting.
Before You Call a Contractor
Having this ready makes the visit faster and the quote more accurate:
Length, width, and ceiling height of each room
Which way each room’s main windows face, and roughly how much glass there is
How well insulated the walls and attic are, if you know
How many people use each room, and whether any room is a kitchen
Whether you will heat with the mini split or only cool
Which rooms you want controlled separately
What to Look for When Hiring an Installer
A room-by-room sizing explanation. Ask how each head was sized, and whether they used a load calculation or a rule of thumb.
Heating capacity at low temperatures, if you will heat with the system, not just the nominal BTU rating.
Multi-zone matching. Confirm the outdoor unit is properly matched to the combined indoor heads.
EPA Section 608 certification for the technician connecting the refrigerant lines.
Final Thoughts
Sizing a mini split starts with square footage, about 20 BTUs per square foot for cooling, and then adjusts for sun, people, kitchens, ceilings, and climate. Working through the worksheet room by room, and getting a load calculation for the tricky rooms, is what makes a mini split quiet, efficient, and comfortable.
Want a contractor to size and price a mini split for your space? Home Services Pros connects homeowners with licensed HVAC installers in their area for free, no-obligation estimates. Call (833) 586-2038 to get started.
Frequently Asked Questions
What size mini split do I need for 500 square feet?
A 500-square-foot room typically needs about 12,000 BTUs, a 1-ton mini split. Add about 10% for a very sunny room, 600 BTUs for each regular occupant beyond two, or 4,000 BTUs if the room is a kitchen.
What size mini split do I need for 1,000 square feet?
About 18,000 BTUs (1.5 tons) for one open 1,000-square-foot area. If that space is divided into separate rooms, several smaller indoor units on a multi-zone system usually work better than one large unit.
How many square feet does a 12,000 BTU mini split cover?
A 12,000 BTU (1-ton) mini split typically cools about 450 to 550 square feet under average conditions. Sunny rooms, high ceilings, more occupants, or a kitchen reduce that coverage.
How many BTUs per square foot does a mini split need?
About 20 BTUs per square foot is a common starting point for cooling. Adjust it for sun, occupancy, kitchens, ceiling height, insulation, and climate, or have a contractor run a load calculation.
How much does a mini split cost for a 500 square foot room?
A 500-square-foot room is usually served by a single 12,000 BTU indoor unit, which falls in the single-zone range of $2,000 to $5,500 installed.
How much does a mini split system cost for 1,000 square feet?
One open 1,000-square-foot area can often be served by a single 18,000 BTU unit, in the single-zone range of $2,000 to $5,500. If those 1,000 square feet are two or three separate rooms, expect a dual- or 3-zone system at $3,500 to $10,000.
How much does a mini split system cost for a 1,500 square foot house?
A 1,500-square-foot house with several separate rooms typically needs three or four zones, which run about $5,500 to $15,000 installed. The exact count depends on how many rooms you want conditioned separately.
Is it bad to oversize a mini split?
A unit far too large for the room short-cycles and leaves the air damp. Inverter mini splits tolerate slight oversizing better than older equipment because they can slow down, so picking the nearest standard size just above the worksheet total is common.
Does a mini split need to be sized for heating too?
If you will heat with it, yes. In colder climates the heating need can exceed the cooling need, so check the unit’s heating capacity at your area’s low temperatures, not just its cooling rating.
