Guides How many BTU do I need for my room
How many BTU do I need for my room
Room area is a starting point, not the whole answer. Two rooms with the same floor area may need very different capacities.
Updated 29 September 2026
Short answer
As a starting point, allow around 130 W per square metre, about 440 BTU per m², in a standard room with a 2.5 m ceiling, and add 100 W per person. A 12 m² bedroom with one person works out at about 5,700 BTU and rounds up to 9,000, the next unit size; a 25 m² living room works out at about 11,400 and rounds up to 12,000.
Increase the capacity if the room is facing west or south, has extensive glazing, is on the top floor or has a high ceiling. Choosing a unit on floor area alone is the most common reason for disappointing results.
The starting table
| Room area | Starting capacity | Typical example |
|---|---|---|
| up to 18 m² | 9,000 BTU | room |
| 19 to 25 m² | 9,000 to 12,000 BTU | large bedroom, office |
| 26 to 33 m² | 12,000 to 18,000 BTU | room |
| 34 to 45 m² | 18,000 to 21,000 BTU | large living room, living room and kitchen together |
| 46 to 52 m² | 21,000 to 24,000 BTU | large room, open-plan space |
| 53 m² or more | own calculation | commercial space, open space |
These values come from the same calculation Clima makes in the calculator on the site: 130 W per square metre, plus 100 W per person, then the next unit size up. They are an honest starting point, not a design. They help you get the order of magnitude before you talk to anyone.
What makes the bill go up
- Solar orientation. A room facing west catches the sun in the hottest hours, and the calculation adds about 15% to the capacity.
- Glass area. Large windows, glazed windows or awnings bring in a lot of heat. Single glass weighs a lot more than double glass.
- Top floor. Under a roof, especially without insulation, the heat that enters through the ceiling is considerable.
- High ceilings. The calculation is made for 2.5 m. At 3 m there is 20% more air for air conditioning.
- Occupation and equipment. Each person adds about 100 W, and a kitchen more than 1,000 W. A meeting room with eight people, or a room with lots of equipment, generates extra heat.
- rooms open to each other. Without a separate door, the real volume is the whole, not the room of the paper.
Why an oversized unit is also bad
It is a less well-known error than that of the small unit, and it is equally expensive.
An oversized unit quickly reaches the required temperature and switches off. Shortly afterwards it switches on again. When working in fits and starts, never manages to dehumidify the air, and it is the humidity, as well as the temperature, that gives the feeling of comfort. You end up with a cold and stuffy room.
Furthermore, starting is the time when a compressor consumes the most and wears out the most. Many short starts mean more consumption and less useful life, with equipment that cost more to buy.
One room or the whole house
If you plan to air-condition more than one room, the bill is no longer the sum of its parts. A system multi-split (several indoor units connected to a single outdoor unit) is usually better than several independent units: a single machine on the façade, one installation, and the capacity distributed among whoever needs it at that moment.
The correct calculation is made on the spot
No table replaces seeing the space. Orientation, glazing, insulation and use change the result enough to justify a visit. The visit is free of charge and so is the quote that comes out of it, and it comes in writing.
If you prefer, work it out here with Clima, or tell us the room’s measurements and orientation through the site assistant or by phone, and we will tell you the right capacity before any commitment.
Need someone to look at this on site?
The site visit and the quote are both free, and the visit is arranged by phone. If it is urgent, call: it is the quickest way. In writing, we reply as soon as the team has the request in hand.