What Size Mini Split Do I Need? MRCOOL DIY® Sizing by Room
- 9K: up to about 350 sq ft
- 12K: about 350–500 sq ft
- 18K: about 500–750 sq ft
- 24K: about 750–1,000 sq ft
- 36K: about 1,000–1,500 sq ft
Sizing a mini split is mostly about one room, its square footage, and a few details that make it harder to heat or cool. Get it right and the unit runs quietly at low speed most of the day, which is where inverter systems are most efficient.
Step 1: measure the space
Length × width of the room (or open area) the unit will serve. Open kitchens and living rooms count as one space. A bedroom behind a closed door is its own space.
| Room size | Start with | Typical spaces |
|---|---|---|
| Up to 350 sq ft | 9K | Bedroom, home office, small shop |
| 350–500 sq ft | 12K | Primary bedroom, bonus room, 1-car garage |
| 500–750 sq ft | 18K | Living room, finished basement, 2-car garage |
| 750–1,000 sq ft | 24K | Open floor plan, large garage, small cabin |
| 1,000–1,500 sq ft | 36K | Big open space, shop, whole small home |
Step 2: adjust for the room
Bump up one size if two or more of these apply:
- Ceilings over 8 ft (vaulted ceilings, lofts)
- Lots of west- or south-facing glass
- Poor insulation: older home, uninsulated garage, metal building
- Hot climate for cooling, or cold winters where it's your main heat
- A kitchen, or lots of people or equipment in the room
Going one size smaller is fine for a well-insulated, shaded room with standard ceilings.
MRCOOLMRCOOL DIY® mini splits explained: which system is right for your spaceBigger isn't better
An oversized unit cools the room fast, shuts down, and starts again. That short cycling wastes energy and leaves the air clammy, because the unit doesn't run long enough to pull out humidity. Inverter systems handle a little extra capacity well, but don't jump two sizes "just in case."
One big unit or two small ones?
A mini split heats and cools the room it's in. It doesn't push air down hallways or into closed bedrooms. If you're trying to cover separate rooms, two smaller indoor units on a DIY® multi-zone condenser almost always beat one big unit in the hallway. Our system builder walks you through it and only shows MRCOOL-approved combos.
Have ductwork already?
If you're replacing an old central system, match the tonnage on your old outdoor unit (24,000 BTU = 2 tons). Our ducted systems page covers the DIY® Hybrid air handler and the Universal® Series up to 5 tons.
Send us the room dimensions, ceiling height, and which way the windows face. We'll tell you what we'd put in our own house. Ask us here, or browse single-zone systems.
Get the DIY Mini Split Install Handbook
All 13 steps, the clearance, torque, wiring and line set tables, QR codes to every MRCOOL video, a sign-off checklist, and a 10% off code for your system.
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