How to calculate how much tile you need
The grout joint changes the count more than you would expect.
Divide the area by the size of one tile plus its grout joint, then add 10 % waste. With a 24 x 12 in tile and a 2 mm joint you get 5.3 tiles per square metre, not 5.4.
The method, step by step
- Measure the real area: length by width of each wall or floor.
- Work out the tile module: (width + joint) x (height + joint).
- Divide the area by the module: that gives the exact tile count.
- Add waste and round up.
Tiles per square metre by format
With a 2 mm joint, standard for indoor work:
Swipe to see the whole table
| Format | Tiles per m² | Ignoring the joint |
|---|---|---|
| 48 x 24 in | 1.34 | 1.35 |
| 24 x 24 in | 2.67 | 2.69 |
| 24 x 12 in | 5.33 | 5.38 |
| 18 x 18 in | 4.72 | 4.78 |
| 12 x 12 in | 10.6 | 10.8 |
| 8 x 8 in | 23.6 | 24.2 |
| 4 x 4 in | 89.1 | 96.9 |
Why the joint matters
A tile does not take up its own size: it takes up its size plus the joint it shares with its neighbours. In large formats the difference is tiny, but with mosaic or small tiles it can mean several tiles per square metre. Ignoring it always makes you over-order, which is the lesser evil, but it also distorts the budget.
From tiles to boxes
Tiles are sold by the box, and the box wins. If you need 71 tiles and a box holds 8, you buy 9 boxes: 72 tiles. That spare is not a rounding error, it is your replacement stock. Ranges get discontinued within a couple of years, and a cracked tile with no spare forces ugly compromises.
Common mistakes
- Measuring only the floor when tiling walls. Each wall is measured separately and the areas added.
- Forgetting untiled areas. In a bathroom, the doorway and sometimes the area behind fitted units take no tile.
- Not asking about the batch. Two boxes of the same model from different batches can vary in shade, and on a big wall it shows.
- Rounding down. 70.7 tiles is 71, never 70.
Sources and methodology
The calculation is geometric: area divided by the module area (tile plus joint), with a configurable waste factor. The recommended waste percentages (10 % straight, 15 % diagonal) are the values commonly used on site.
Frequently asked questions
How many 12x12 tiles in a square metre?
10.6 tiles with a 2 mm joint, which is 0.98 per square foot. Ignoring the joint would give 10.8.
How do I calculate tiles for a bathroom?
Measure each wall separately (length by height), add the areas, subtract the door and window if they are not tiled, then apply the same module-plus-waste method.
How many boxes of tile do I need?
Divide the total tiles by the tiles per box and round up. If the box states coverage in square feet instead, divide the area including waste by that coverage.
Should I subtract doors and windows?
On walls, yes, because no tile goes in the opening. On floors, only subtract fixed elements that genuinely take up area.
What joint width should I use?
1.5 to 3 mm indoors with rectified tiles, and 3 to 6 mm outdoors or with non-rectified tiles. The joint absorbs substrate movement.