What Size Aircon Do I Need in Thailand? BTU by Room Size
Figures reviewed 14 October 2026
The short answer
In Thailand, plan for about 770–880 BTU per square metre of floor area. That's a starting range of 700–800 BTU/m² with 10% added for the hot, humid climate. This assumes a normal 2.4 m ceiling, two people and partial sun.
A 20 m² bedroom (4 × 5 m) therefore needs 15,400–17,600 BTU/h. The next standard size up is an 18,000 BTU unit.
Use this Thailand-adjusted table as a starting estimate, then check the room’s sun exposure, ceiling height, occupants and layout before choosing a unit.
BTU by room size
| Aircon size | Room size (m²) | Room size (ft²) | Typical room |
|---|---|---|---|
| 9,000 BTU | 10.2–11.7 | 110–126 | Small bedroom, home office |
| 12,000 BTU | 13.6–15.6 | 146–168 | Standard condo bedroom |
| 18,000 BTU | 20.5–23.4 | 221–252 | Master bedroom, studio condo |
| 24,000 BTU | 27.3–31.2 | 294–336 | Living room, open-plan studio |
| 30,000 BTU | 34.1–39.0 | 367–420 | Large living/dining area |
Each range reflects the 700–800 BTU/m² baseline under partial sun and a 2.4 m ceiling. Shade and strong sun are separate adjustments; strong sun means less floor area for the same rated unit.
Adjust for your actual room
The calculator applies these adjustments:
Selecting strong sun adds 15%. Large glass is a reason to ask the installer for a site check, not an automatic extra 15% in the calculator. The climate, sun and ceiling percentages add against the same 700–800 BTU/m² base; they are not multiplied together.
Well-shaded room: subtract 10%.
High ceiling: add 10% for every 0.3 m above 2.4 m.
More than two people regularly in the room: add 600 BTU per extra person.
Kitchen: add 4,000 BTU.
Rooms directly under the roof often run hotter, especially in older houses with little insulation. The calculator doesn't add a fixed amount for this, because insulation varies so much. If the ceiling feels hot to the touch in the afternoon, mention it to your installer.
Why bigger isn't automatically better
An oversized unit cools the air quickly, then switches off before it has removed the moisture. This is called short cycling. The room ends up cold but clammy, which matters in Thailand's humidity.
Inverter units cope with this better than older fixed-speed units, but sizing far above your room's needs still wastes money upfront.
Before you buy or accept a quote
Ask the installer for these in writing:
Model code, so you can check the BTU rating and energy label yourself.
Installation price, including how many metres of copper pipe are included. Extra metres are usually charged separately.
Electrical work: whether the unit needs a new circuit or breaker.
Placement: where the indoor unit and outdoor compressor will go. Condo buildings often have rules about compressor locations.
FAQ
Is one big unit better than two small ones for an open-plan room? Their combined BTU is only a starting point. Airflow and placement matter as much. Two units can cool an L-shaped room more evenly.
My rental's aircon struggles. Is it too small? Check that the filters are clean and the unit has been serviced recently. Dirty filters and low refrigerant are common causes. If it's serviced and still can't cope, compare its BTU rating (on the indoor unit's label) with the table above.
Calculate BTU for a 4 × 5 m room