How it works
Enter the room's width and length (or area in m²), choose the room type and whether it gets sun. You get the BTU needed and the nearest standard AC size sold in Thailand. The table shows roughly what room size each AC size suits under your conditions.
Formula
BTU = room area (m²) × factor
| Room type | Little sun | Sunny |
|---|---|---|
| Bedroom (used at night) | 700 | 800 |
| Living room / office (used by day) | 750 | 850 |
| Shop / restaurant / meeting room | 900 | 1000 |
Ceilings above 3 m scale up in proportion to height · each person beyond 2 adds 600 BTU
This is an estimate for choosing a unit. Have an installer survey the room before installation.
FAQ
How many BTU for a 4×4 m bedroom?
A 16 m² room with little sun needs about 16 × 700 = 11,200 BTU, so choose a 12,000 BTU unit. If it gets afternoon sun or is a top-floor room under the roof, use 16 × 800 = 12,800 BTU and choose 13,000 BTU.
Can I buy a bigger AC than needed?
Not much bigger. An oversized unit cools quickly and cycles off often, so it removes less humidity (cold but clammy) and wastes power at start-up. An undersized unit runs flat out all the time, never cools enough and also wastes power.
Why do sunny rooms need more BTU?
Sun-heated walls and roofs store heat and radiate it into the room, especially west-facing walls, large windows and top-floor rooms under the roof. Choose "Sunny" for these.
Is BTU sizing different for inverter ACs?
No. Inverter units can vary compressor speed, so they cope better when the size is not exact and use less power when running for long periods, but you should still size them to the room.