Case 1
- Floor area
- 20m²
- Tile length
- 30cm
- Tile width
- 30cm
- Waste allowance
- 10%
245tiles
Open with these valuesTile Calculator
245tiles
Result: 245 tilesFloor area divided by the area of one tile, times the waste factor, rounded up. 20 m² with 30 × 30 cm tiles is 222.2 tiles; at 10 % waste that is 245. The allowance is applied before the rounding, not after — rounding first would order an extra tile for nothing.
The numbers at a glance
Held fixed: Floor area 20.00 m², Tile length 30.0 cm, Tile width 30.0 cm.
| Waste allowance (%) | Result (tiles) |
|---|---|
| 0 | 223 |
| 3 | 228 |
| 5 | 234 |
| 8 | 239 |
| 10Your value | 245 |
| 13 | 250 |
| 15 | 256 |
| 18 | 262 |
| 20 | 267 |
Worked examples
Case 2
- Floor area
- 10m²
- Tile length
- 60cm
- Tile width
- 60cm
- Waste allowance
- 10%
31tiles
Open with these valuesCase 3
- Floor area
- 15m²
- Tile length
- 20cm
- Tile width
- 20cm
- Waste allowance
- 0%
375tiles
Open with these valuesHow it's calculated
tiles = ⌈area ÷ tile area × (1 + waste)⌉
- StepEnter the floor area in square metres — length × width for a rectangle.
- StepEnter one tile's length and width in centimetres, ignoring the grout.
- StepSet the waste allowance: 10 % for a straight layout, 15–20 % diagonal.
- ResultThe count rounds up to whole tiles; keep the spares for repairs.
What this number means
Cuts eat whole tiles, not offcuts
Every tile that meets a wall or a corner has to be cut, and the piece that comes off is rarely the right shape for anywhere else. That is what the waste allowance pays for, and why a room with many corners needs more of it.
Where the 10 % allowance comes from
The tile merchant's page behind this calculator recommends an extra 10 % on top of your exact square meterage and calls it the 10 % rule. Diagonal and herringbone layouts, and rooms with many corners, want 15 to 20 % instead.
Grout joints are left out, in your favour
The count works from the bare tile size, but a laid tile occupies that size plus its joint. Leaving the joint out therefore overstates the tile count slightly, and that small surplus sits on top of the waste allowance.
The allowance goes on before the rounding
20 m² of 30 × 30 cm tiles is 222.2 tiles, and 10 % on top makes 244.4, which rounds up to 245. Round to 223 first and add the 10 % afterwards and you land on 246 — one tile bought for nothing.
Commonly misread
20 m² divided by 0.09 m² per tile is 223, so I ordered 223.
That is the bare count, with nothing cut and nothing broken. Add the 10 % allowance and the order is 245 tiles.
I entered the tile size in metres, as 0.3 by 0.3.
Both tile fields are centimetres, so a 30 cm tile goes in as 30. The conversion to square metres happens inside the formula.
The result was 245, so I ordered 24 boxes of ten and one loose tile.
Tiles leave the shop by the full box, so 245 in boxes of ten means 25 boxes. Keep the five spare tiles for later repairs.
Reference table
| Area, tile length, tile width, waste | One tile | Tiles |
|---|---|---|
| 8, 20, 20, 10 | 0.04 m² | 220 |
| 10, 60, 60, 10 | 0.36 m² | 31 |
| 12, 45, 45, 10 | 0.2025 m² | 66 |
| 15, 20, 20, 0 | 0.04 m² | 375 |
| 20, 30, 30, 10 | 0.09 m² | 245 |
Questions
How many tiles do I need?
Divide the floor area by the area one tile covers, multiply by the waste factor, then round up. A 20 m² floor with 30 × 30 cm tiles, each 0.09 m², needs 20 ÷ 0.09 × 1.10, which is 245 tiles at 10 % waste.
How much waste should I add?
10 % is the usual rule of thumb for a straight, grid-aligned layout, and the source behind this calculator recommends exactly that. Raise it to 15–20 % for diagonal or herringbone layouts and for rooms with many corners, because every cut wastes part of a tile.
Why does the result round up to a whole tile?
Because you can only buy whole tiles — half a tile still means buying one and cutting it. The calculator rounds the final figure up so you are never short on the day.
Does it account for grout lines?
No. It uses the bare tile size, which slightly overestimates the count because a tile plus its grout gap takes a little more space. That small surplus works in your favour on top of the waste allowance.
Tiles are sold by the box — how do I convert?
Divide the tile count by the number of tiles per box and round up. For 245 tiles in boxes of 10 that is 25 boxes. Boxes also state their coverage in m², so you can cross-check against your floor area.
Sources and last check
Information, not professional advice.