Mini Split Calculator (Metric)
Find the BTU capacity a ductless mini-split needs to heat and cool your space, based on room size, ceiling height, and your climate.
What your result means
BTU needed is the cooling and heating capacity your room requires, from its floor area and ceiling height, scaled for your climate. Recommended unit rounds up to the nearest standard mini-split size. Bigger is not better — an oversized unit short-cycles and dehumidifies poorly. To price the install, use our heat pump cost calculator, or our HVAC size calculator for whole-home systems.
How to use this calculator
- Measure the room or zone in square feet.
- Enter the ceiling height (2.4 m is standard).
- Pick your climate — mild, moderate, or an extreme hot or cold area.
- Read the BTU needed and the recommended standard unit size.
- Adjust up for lots of windows, sun, or a kitchen; down for shaded rooms.
The formula
Mini-splits are sized in BTU. A common baseline is about 20 BTU per square foot, nudged up for hot or cold climates and tall ceilings, then rounded to the nearest standard unit (9k, 12k, 18k, 24k, and so on).
Worked example
A 37.2 m² room with 2.4 m ceilings in a moderate climate needs about 400 times 22, or 8,800 BTU. The nearest standard unit at or above that is 9,000 BTU — a 0.75-ton mini-split. A sunny room or one with a big west window might bump you to the 12,000 BTU size.
Mini-split sizing guide (moderate climate)
| Room size | Approx. BTU | Common unit |
|---|---|---|
| 150 - 32.5 m² | 6,000 - 9,000 | 9,000 BTU |
| 350 - 51.1 m² | 9,000 - 12,000 | 12,000 BTU |
| 550 - 1,0 m² | 12,000 - 18,000 | 18,000 BTU |
| 1,000 - 1,37.2 m² | 18,000 - 24,000 | 24,000 BTU |
| Multiple rooms | Add zones | Multi-zone outdoor unit |
Tips & gotchas
- Don't oversize. A too-big mini-split short-cycles, wastes power, and leaves the room clammy.
- Add roughly 10% BTU for rooms with heavy sun or lots of glass.
- Kitchens need extra capacity — add about 4,000 BTU for the heat load.
- For several rooms, a multi-zone outdoor unit with separate heads beats one big head.
- BTU sizing is the start; the install cost depends on line-set length and electrical.
Frequently asked questions
What size mini split do I need for 37.2 m²?
About 9,000 BTU in a moderate climate. Bump to 12,000 BTU if the room is sunny, has a vaulted ceiling, or sits in a hot climate.
How many BTU per square foot for a mini split?
Roughly 18 to 28 BTU per square foot depending on climate, with about 20 to 22 as a common baseline for moderate areas.
Is it bad to oversize a mini split?
Yes. An oversized unit cools too fast, short-cycles, and doesn't dehumidify well, which wastes energy and feels clammy. Size it to the room.
Can one mini split do a whole house?
Usually not. Mini-splits are zone-based. For a whole house, use multiple heads on a multi-zone outdoor unit, sized room by room.
What does a mini split cost to install?
Ductless systems commonly run $5 to $8 per square foot installed. Use our heat pump cost calculator to estimate your job.
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