The formula, and the unit trap
One square metre is 10,000 cm². Divide it by the area of one tile in cm² and you have the count. That is the whole calculation.
tiles per m² = 10 000 ÷ (width cm × height cm)
The trap is mixing units. A 30 × 60 tile is 1 800 cm², not 18 m² and not 0.18 anything. Convert once, at the start, and stay in one system. Half the wrong orders in tiling come from someone dividing metres by centimetres and being off by a factor of a hundred.
Tiles per square metre by size
| Tile size | Area of one tile | Tiles per m² |
|---|---|---|
| 10 × 10 cm | 100 cm² | 100 |
| 15 × 15 cm | 225 cm² | 44.4 |
| 20 × 20 cm | 400 cm² | 25 |
| 7.5 × 15 cm (metro) | 112.5 cm² | 88.9 |
| 10 × 30 cm | 300 cm² | 33.3 |
| 20 × 50 cm | 1 000 cm² | 10 |
| 25 × 40 cm | 1 000 cm² | 10 |
| 30 × 30 cm | 900 cm² | 11.1 |
| 30 × 60 cm | 1 800 cm² | 5.6 |
| 45 × 45 cm | 2 025 cm² | 4.9 |
| 60 × 60 cm | 3 600 cm² | 2.8 |
| 75 × 75 cm | 5 625 cm² | 1.8 |
| 80 × 80 cm | 6 400 cm² | 1.6 |
| 120 × 60 cm | 7 200 cm² | 1.4 |
| 120 × 120 cm | 14 400 cm² | 0.7 |
These are nominal counts and they are what suppliers use. They ignore the grout joint, which is correct for ordering — see below for why.
Does the grout joint change the count?
Physically yes, practically no, and it is worth understanding why so you do not accidentally under-order.
A 60 × 60 tile with a 3 mm joint occupies 60.3 × 60.3 cm of floor, so you need slightly fewer tiles — about 2.75 instead of 2.78 per m². That is a 1% saving. Meanwhile the waste allowance you should be applying is 10-20%. The joint is noise inside a much larger correction, and it works in the safe direction anyway.
One exception: mosaic and very small formats. A 2 × 2 cm mosaic with a 2 mm joint is 33% larger per piece once grouted, and there the joint genuinely matters. This is also why mosaic is sold by the sheet, with the sheet coverage printed on the box — use that figure, not a tile count.
Never subtract the joint to reduce an order. The 1% you save is inside the rounding, and if the tiler uses a 2 mm joint instead of 3 you are short.
From square metres to boxes
Boxes are what you actually buy, and box coverage varies by manufacturer even for identical tile sizes — a 60 × 60 box might hold 3, 4 or 6 pieces depending on thickness and who made it. The number printed on the box is coverage in m², and that is the only number you need.
boxes = ceiling( area with waste ÷ box coverage m² )
| Tile size | Typical pieces per box | Typical box coverage |
|---|---|---|
| 20 × 20 cm | 25 | 1.00 m² |
| 30 × 30 cm | 11 | 1.00 m² |
| 30 × 60 cm | 8 | 1.44 m² |
| 45 × 45 cm | 7 | 1.42 m² |
| 60 × 60 cm | 4 | 1.44 m² |
| 80 × 80 cm | 2 | 1.28 m² |
| 120 × 60 cm | 2 | 1.44 m² |
These are typical, not standard. Always read the coverage on the actual box you are buying. Two 60 × 60 ranges in the same shop can differ by 30% per box.
A worked example
A kitchen floor, 4.2 × 3.0 m, in 60 × 60 porcelain, straight set, boxes covering 1.44 m².
area = 4.2 × 3.0 = 12.6 m²
tiles per m² = 10 000 ÷ 3 600 = 2.78
tiles, no waste = 12.6 × 2.78 = 35
with 12% waste = 12.6 × 1.12 = 14.1 m²
boxes = 14.1 ÷ 1.44 = 9.8 → 10 boxes
Ten boxes is 14.4 m² and 40 tiles. You measured 12.6 m² and will lay about 35 whole tiles plus cuts. The five spare tiles are the point, not an error — one is the future repair, the rest absorb the two you will crack cutting the doorway.
Checks before you order
- Divide the room length by the tile length and look at the remainder. A remainder under 10 cm means a thin sliver along one wall that is hard to cut and looks bad. Shifting the start line by half a tile usually fixes it and costs nothing.
- Check whether the size on the label is nominal or actual. A tile sold as 60 × 60 is often 59.6 × 59.6 rectified, or 59.3 × 59.3 pressed. It does not change the order, but it changes where your last cut lands.
- Rectangular tiles have a direction. Laying a 30 × 60 the long way versus the short way changes the number of cuts, not the area — but it can change the waste by several percent.
- Confirm the box coverage in m² on the physical box, not the website. Listings are frequently wrong or list the piece count only.
- Order everything at once, from one batch. Calibre and shade codes vary between production runs.