How many BTU for a 12 m² bedroom?

With a ceiling no higher than 3 m, a 12 m² bedroom needs 9,600 BTU/h. The wall unit that does not fall short of that is the MSY-GZ13VF at 12,624 BTU/h.

Why not just buy a much bigger unit?

An oversized unit cycles on and off too often and does not pull the humidity out, so the app warns when the unit you placed is much bigger than the room needs.

What about a high ceiling?

Above 3.00 m, scale up by the extra height: a 4.50 m ceiling multiplies by 1.5. A ceiling lower than 3.00 m counts as 3.00 m.

BTU

Air-con BTU calculator

An 18 m² bedroom with a ceiling up to 3 m needs 14,400 BTU/h, at 800 BTU per square metre. A living room takes 900 and a home office 1,000.

Enter the room size and ceiling height, say what the room is for, and see how many BTU it needs and which unit cools it enough. The formula and the units are the manufacturer's published figures, the same ones the RAYA app uses.

BTU calculator

14,400 BTU/h

18.00 m² × 800 BTU/m² = 14,400 BTU/h

Wall unit: MSY-GZ18VF 17,742 BTU/h
4-way ceiling cassette: PLY-M18EA2 18,084 BTU/h

The unit shown is the smallest that does not fall short of what the room needs. If even the largest is not enough, it says how many units it takes.

Formula

Area, room type and ceiling height

The BTU a room needs is its area times a factor for the kind of room: 800 for a bedroom, 900 for a living room, 1,000 for a home office and 1,100 for a restaurant, in BTU per square metre.

The formula assumes a 3.00 m ceiling. A lower ceiling does not reduce the figure; a higher one scales it up in proportion, so 4.50 m multiplies by 1.5.

The factors come from Mitsubishi Electric Kang Yong Watana's BTU calculator, and each unit's BTU is the capacity the manufacturer publishes, not the round number on the box. Retrieved 20 Sep 2026.

Common room sizes, ceiling up to 3 m
Area	Bedroom	Living room
9 m²	7,200 BTU/hMSY-GZ09VF · 9,554	8,100 BTU/hMSY-GZ09VF · 9,554
12 m²	9,600 BTU/hMSY-GZ13VF · 12,624	10,800 BTU/hMSY-GZ13VF · 12,624
15 m²	12,000 BTU/hMSY-GZ13VF · 12,624	13,500 BTU/hMSY-GZ15VF · 14,330
18 m²	14,400 BTU/hMSY-GZ18VF · 17,742	16,200 BTU/hMSY-GZ18VF · 17,742
20 m²	16,000 BTU/hMSY-GZ18VF · 17,742	18,000 BTU/hMSY-GZ24VF · 22,519
25 m²	20,000 BTU/hMSY-GZ24VF · 22,519	22,500 BTU/hMSY-GZ24VF · 22,519
30 m²	24,000 BTU/hMSY-GZ30VF · 27,978	27,000 BTU/hMSY-GZ30VF · 27,978

Limits

What this figure leaves out

Rooms in strong sun, facing west, or on the top floor under the roof: the manufacturer publishes no factor for them, so nothing is added.
Offices and shops: the manufacturer's calculator only covers the four room types above.
Before you buy, have an air-con technician look at the room.

In the app

Place the unit on the plan and let the app work it out

In the RAYA app, put an air-con unit in the room you drew. Its card works out the BTU from the room's real area with the same formula, suggests a model, and warns if the unit is too small or too big for the room.

See a real room in Design your own home

Wall air-con card: bedroom 16.97 m² × 800 BTU/m² = 13,576 BTU/h, suggested model MSY-GZ15VF at 14,330 BTU/h — Air-con, BTU worked out

FAQ

Questions about air-con BTU

How many BTU for a 12 m² bedroom?: With a ceiling no higher than 3 m, a 12 m² bedroom needs 9,600 BTU/h. The wall unit that does not fall short of that is the MSY-GZ13VF at 12,624 BTU/h.
Why not just buy a much bigger unit?: An oversized unit cycles on and off too often and does not pull the humidity out, so the app warns when the unit you placed is much bigger than the room needs.
What about a high ceiling?: Above 3.00 m, scale up by the extra height: a 4.50 m ceiling multiplies by 1.5. A ceiling lower than 3.00 m counts as 3.00 m.

Terms

Terms on this page

More words you meet when doing up a home are in the Interior design glossary

Arrange your first room

You can start from a sample room. Stuck anywhere? Message us on LINE @raya-studio or see plan prices on the home page

Open app