Work out how many tiles and boxes you need for a floor or wall, including cutting waste.
Getting the tile count right
Start from the area to cover, divide by the area of one tile, then add waste. Ten percent is the usual allowance for a simple rectangular room laid straight; allow fifteen to twenty for diagonal or herringbone layouts, or for rooms with many corners and cut-outs, because every cut leaves an offcut you cannot use elsewhere.
Buy all your tiles in one go and check that the boxes share the same batch number: colour varies slightly between production runs, and a box bought later can be visibly different. Keeping a spare box after the job is worth it for future repairs, since discontinued ranges are hard to match.
One centimetre wider and the same room needs 27 more tiles
A room of 3.60 by 4.20 metres takes exactly 168 tiles of 30 cm with not a single cut — both dimensions divide cleanly. Make it 3.61 by 4.21 and you need 195 tiles and 27 cuts, because a three-millimetre sliver still costs a full row and a full column. Tile counts do not rise smoothly with area; they jump at every multiple.
How it works
- Counts tiles by row and column rather than by dividing area, which is what the cuts depend on.
- Separates whole tiles from cut ones, since the cut ones drive both labour and waste.
- Adds a waste allowance appropriate to the laying pattern and converts to boxes.
columns = ⌈room width ÷ tile width⌉ rows = ⌈room length ÷ tile length⌉ tiles = columns × rows whole tiles = ⌊width ÷ tile⌋ × ⌊length ÷ tile⌋ cut tiles = tiles − whole tiles waste: straight 10%, diagonal 15%, herringbone 20%
Worked example
The same 30 cm tile in four room sizes that differ only slightly.
- 3.30 × 4.20 m → 11 × 14 = 154 tiles, 0 cuts
- 3.60 × 4.20 m → 12 × 14 = 168 tiles, 0 cuts
- 3.40 × 4.20 m → 12 × 14 = 168 tiles, 14 cuts
- 3.61 × 4.21 m → 13 × 15 = 195 tiles, 27 cuts
One centimetre in each direction turns a cut-free job into 27 tiles of cutting and 27 extra tiles bought. The area rose by less than half a percent; the tile count rose by 16%.
Reading the result
- Measure the room properly before ordering, because the arithmetic is a step function. Rounding 3.61 down to 3.6 on the order form is exactly the assumption that leaves you a column short on the last day.
- Waste allowance sits on top of the counted tiles, not instead of them. A straight lay wants about 10%, a diagonal lay 15% and herringbone 20% — every cut at an angle produces an offcut that fits nowhere else.
- For the same room laid straight, 168 tiles becomes 185 at 10%, 194 at 15% and 202 at 20%. The pattern you choose costs more in material than most people budget for, before any labour difference.
- Order whole boxes and keep the spares. Tiles are made in batches with slight colour variation, so a replacement bought two years later rarely matches — the leftovers from the original box are the only exact match you will ever have.
Common questions
- Why not just divide the floor area by the tile area?
- Because that ignores cuts. A 3.61 by 4.21 m room is 15.2 m², which by area is 169 tiles; laid out in rows and columns it needs 195. The difference is the partial row and partial column, each of which consumes whole tiles.
- How much waste should I add?
- About 10% for a straight lay, 15% for diagonal and 20% for herringbone. The figure rises with the number of angled cuts rather than with the area, which is why a complex pattern in a small room can waste proportionally more than a simple one in a large room.