How to calculate how many tiles you need
- Measure the area in metres and multiply length by width: a 4 × 3 m floor is 12 m².
- Work out the area of one tile in m² by multiplying its sides in cm and dividing by 10,000: 30 × 60 cm = 1,800 cm² = 0.18 m².
- Divide the area by the tile area: 12 ÷ 0.18 = 66.7 tiles.
- Add a waste allowance for cuts and breakage. With 10%: 66.7 × 1.10 = 73.3, so round up to 74 tiles.
- Divide by the number of tiles per box and round up again: with 8 tiles per box, 74 ÷ 8 = 9.25, so buy 10 boxes.
Always round up at the end, not at every step. Many tiles are also sold by the square metre — then divide the area including waste by the m² per box: 13.2 m² ÷ 1.44 m² = 9.2, so 10 boxes.
Tiles per square metre for common tile sizes
| Tile size | Area of one tile | Tiles per m² | Tiles for 10 m² + 10% |
|---|---|---|---|
| 10 × 10 cm | 0.01 m² | 100 | 1,100 |
| 15 × 15 cm | 0.0225 m² | 44.4 | 489 |
| 20 × 20 cm | 0.04 m² | 25 | 275 |
| 20 × 40 cm | 0.08 m² | 12.5 | 138 |
| 30 × 30 cm | 0.09 m² | 11.1 | 123 |
| 30 × 60 cm | 0.18 m² | 5.56 | 62 |
| 60 × 60 cm | 0.36 m² | 2.78 | 31 |
| 60 × 120 cm | 0.72 m² | 1.39 | 16 |
Tiles per m² = 10,000 ÷ (length × width in cm). Grout joints are not included, so the real number is slightly lower.
How much extra tile to buy
| Layout or room | Extra tile |
|---|---|
| Straight layout in a simple, rectangular room | 10% |
| Diagonal, herringbone, basketweave or mosaic patterns | 15% |
| L-shaped rooms or rooms with curved walls | 15–20% |
| Diagonal layout in a small room with many cuts | up to 25% |
Source: CLE Tile, “How much extra tile to buy”.
Large-format tiles leave bigger offcuts that often cannot be reused, so use the upper end of the range for them. Rooms with many pipes, a floor drain or boxed-in corners also need more cuts.
Tiling walls: subtract doors and windows
For walls, multiply the length of each wall by the height to be tiled and add the walls together. A small bathroom of 2 × 1.5 m tiled to 2.4 m has 2 × (2 + 1.5) × 2.4 = 16.8 m² of wall. Subtract the door (0.8 × 2.0 m = 1.6 m²) and you get 15.2 m².
With 20 × 40 cm wall tiles (0.08 m²) that is 15.2 ÷ 0.08 = 190 tiles, or 209 with 10% waste. Work out the floor separately — floor and wall tiles are usually different products.
Tiles in square feet
In the US, tile sizes are given in inches and boxes in square feet. A 12 × 12 in tile is exactly 1 ft², and a 12 × 24 in tile is 2 ft². A 150 ft² floor with 12 × 24 in tiles needs 150 ÷ 2 = 75 tiles, or 83 with 10% waste. To convert, 1 m² = 10.764 ft².
Do grout joints change the number of tiles?
Slightly. A joint makes each tile take up a little more space: a 30 × 30 cm tile with a 3 mm joint covers 30.3 × 30.3 cm, so you need 10.9 tiles per m² instead of 11.1 — about 2% fewer. The waste allowance more than covers this, which is why the calculator ignores joints. To work out how many kilos of grout to buy, use the Grout Calculator.
Before you buy
- Buy all the tiles, including the spares, at the same time. Batches can vary slightly in shade and finish, even within the same product line.
- Keep a box or a few spare tiles after the job. Tiles get discontinued, and an exact match can be impossible to find when one cracks years later.
- Lay out the first rows dry before you start, so you can see where the cuts will fall and avoid thin slivers at the edges.