Tile Calculator
The wastage allowance is the part people skip, and it is the reason so many tiling jobs stop one box short.
The calculation
Both the tile count and the box count round up. You cannot buy nine tenths of a tile, and you cannot buy most of a box.
Worked example: a 4.2 × 3.0 m floor is 12.6 m². With 60 × 30 cm tiles at 0.18 m² each, that is 70 tiles exactly. Add 10 % wastage and you need 77, which at 8 per box means 10 boxes — giving 80 tiles and 3 spare.
Choosing a wastage allowance
| Situation | Allowance |
|---|---|
| Simple rectangular room, straight lay | 10 % |
| Room with alcoves, pipes or awkward corners | 15 % |
| Diagonal laying | 15–20 % |
| Herringbone or complex pattern | 20–25 % |
| Large-format tiles (cuts waste more material) | 15 % |
| Patterned tiles needing alignment | 20 %+ |
Two reasons the allowance is not optional. Cutting produces offcuts that rarely fit anywhere else, and tiles break — both in transit and while being cut. Beyond that, keeping a few spare tiles after the job is genuinely valuable: tile ranges are discontinued constantly, and a cracked tile in three years' time is much easier to replace from a box in the loft than from a shop.
Buy all boxes at once and check the batch number. Colour varies noticeably between production batches, especially on natural stone and glazed ceramics.
What else the job needs
Tiles are one line of the shopping list. For a typical 12 m² floor you will also need:
- Adhesive: roughly 4–6 kg per m² for floors, 3–4 for walls. Around three 20 kg bags for this job.
- Grout: depends on tile size and joint width — typically 0.5–1 kg per m² for standard joints, more for small tiles or wide joints.
- Spacers in the chosen joint width, usually 2–3 mm for walls and 3–5 mm for floors.
- Trim or edging for exposed edges, measured in linear metres.
- Primer for porous or dusty substrates, and decoupling membrane over underfloor heating or timber.
Plan the layout before fixing anything: starting from the centre and working outwards gives symmetrical cuts at both edges, which looks far better than a full tile at one wall and a 2 cm sliver at the other.
Frequently asked questions
Should I measure the room or the tiles first?
The room, and measure it in several places. Rooms are rarely square, and the difference between the widest and narrowest point determines how much cutting is needed along each wall — which is exactly what the wastage allowance covers.
How many spare tiles should I keep?
Enough to repair a small area: five to ten tiles for a typical room, or about 2 % of the total. Ranges get discontinued, and an exact match later is often impossible.
Does tile size affect wastage?
Yes. Large-format tiles waste more per cut because each offcut is bigger, so allow 15 % rather than 10. Small mosaic sheets waste less, since sheets can often be trimmed to fit.