Air Conditioner BTU Calculator
Pick the right air conditioner size for any room in seconds. Enter the width and length in metres, choose whether it is a bedroom, living room or office/shop, tick the box if the room is hot or sun-exposed, and optionally set the ceiling height. The tool works out the room area, applies a BTU-per-square-metre factor for that room type, adds a heat-load allowance and adjusts for ceiling height, then shows a recommended BTU range and the nearest common AC size — 9,000, 12,000, 18,000, 24,000, 30,000 or 36,000 BTU. Everything runs in your browser, so nothing is uploaded.
The shorter side of the room, measured in metres.
The longer side of the room, measured in metres.
Rooms with more people, appliances or activity need more cooling per square metre.
Tick this if the room faces the afternoon sun, has a west/top-floor wall, a large window or a metal roof — it adds about 18% more BTU.
Leave blank for a standard 2.6 m ceiling. Taller ceilings mean more air to cool, so the BTU scales up.
Your recommended AC size will appear here
Enter the room width and length to get a suggested air conditioner BTU size.
Room area Width multiplied by length.
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Recommended BTU Cooling capacity range for this room, based on area, use, heat load and ceiling height.
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Suggested AC size The nearest common air conditioner size that covers the higher end of the recommended range.
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Suggested air conditioner
Common Thai AC sizes are 9,000 / 12,000 / 18,000 / 24,000 / 30,000 / 36,000 BTU. Choosing the size just above your requirement gives comfortable cooling without wasting energy.
Tips
This is an estimate only. The actual BTU you need also depends on insulation, number of occupants, appliances, window size and direction, and how often doors open. Treat the result as a starting point and confirm with a professional installer.
How to use
- Measure the room and enter its width and length in metres.
- Choose the room use: bedroom, living room, or office/shop.
- Tick "hot or sun-exposed room" if it faces the sun or has a hot roof.
- Optionally set the ceiling height if it is not the standard 2.6 m.
- Read the room area, recommended BTU range and suggested AC size instantly.
- Review the tips, then copy the result to compare models when you buy.
Features
- Recommends a BTU range and maps it to the nearest common Thai AC size
- Separate cooling factors for bedrooms, living rooms and offices/shops
- Heat-load option adds about 18% for sun-exposed or hot rooms
- Optional ceiling-height adjustment for taller-than-standard rooms
- Flags very large rooms and suggests two units instead of one oversized unit
- 100% in-browser — your measurements are never uploaded or stored