Tiling a room? Here is how Thai tile makers and building-supply stores work out how many tiles and boxes to buy, with an example. Or let the tile calculator do it.
In short
- Find the room's area in square metres (width × length).
- Divide by the area of one tile, in square metres.
- Add 5–10% for cutting waste, then round up to a whole number.
- Divide by the tiles per box printed on the box, and round up again.
SCG's method
SCG explains: divide 1 square metre by the tile's size. A 30×45 cm tile is 0.30 × 0.45 m, so 1 ÷ 0.135 = 7.407 tiles per square metre; multiply by the room's area.
SCG rounds 7.407 to 7.4 first and gets 7.4 × 20 = 148 tiles for a 20 m² room. Without that early rounding it is 148.15. Our calculator keeps the exact figure and rounds up once at the end, giving 149, so you never run short.
Tiles per square metre by size
| Size (cm) | Tiles per m² (1 ÷ tile area) | Tiles per box in SCG's table |
|---|---|---|
| 20×20 | 25 | 25 |
| 30×30 | 11.11 | 11 |
| 40×40 | 6.25 | 6 |
| 50×50 | 4 | 4 |
| 60×60 | 2.78 | 4 |
| 30×45 | 7.41 | 8 |
| 30×60 | 5.56 | 8 |
Tiles per box vary by brand and model, so always check the box or product page. For example, one 60×60 tile at Thai Watsadu comes 4 to a box, covering 1.44 m².
Example
A 4 × 5 m room = 20 m², with 60×60 cm tiles:
- Tile area 0.6 × 0.6 = 0.36 m²
- 20 ÷ 0.36 = 55.56 tiles
- 10% extra: 55.56 × 1.10 = 61.11 → buy 62 tiles
- 4 per box: 62 ÷ 4 = 15.5 → buy 16 boxes
How much extra to buy
The sources differ:
- SCG: at least 5–10%, depending on how hard the pattern is and the room's shape (square, many corners, diagonal, curved, round).
- COTTO: about 5–10% of what you use, kept for future repairs.
- Boonthavorn: about 10–15%, for breakage in transport or laying, cutting to fit, and repairs.
A plain rectangular room laid straight can use the low end; many corners, a diagonal pattern or large tiles call for more. Our calculator starts at 10%, and you can change it.
Rooms that aren't rectangles
Thai Soung and Boonthavorn suggest splitting an L-shaped or complicated room into rectangles, working out each area and adding them up, with a little more extra than usual. Area of shapes can help.
Buy everything at once, from one lot
- SCG notes that if you run short and buy more, you may not get the same lot, and the difference in shade shows once laid.
- COTTO explains that shades vary with firing temperature and raw materials, and suggests noting the code, grade, shade and colour on the box.
- Thai Soung suggests checking that the shade and lot number on every box match.
Grout joints
- COTTO recommends joints of at least 3 mm, or at least 2 mm for rectified tiles.
- Thai Soung suggests at least 2 mm for rectified tiles and about 2–5 mm for standard or large tiles.
Joints slightly reduce the number of tiles needed, so ignoring them errs on the safe side.
Note
This article is based on web pages from SCG HOME, COTTO, Thai Soung and Boonthavorn and a Thai Watsadu product page, read on 29 September 2026. The figures are estimates for shopping; have your tiler check the room before you order.
