Where tile waste actually comes from
Almost all of it is one thing: the offcut you cannot use anywhere else.
Cut a tile to fill a 60 mm gap at a wall and you are left with a piece 240 mm wide. If the opposite wall happens to need 240 mm, you have lost nothing. It almost never does. So the offcut goes in the skip, and the waste factor is the allowance for how often that happens.
Everything else is secondary — a few cracked in transit, one dropped, one cut wrong. Real, but small next to the geometry.
The figures, and why they differ
- Straight grid: 10 per cent. Cuts happen only at the perimeter, and offcuts from one side often serve the other.
- Brick or offset bond: 10 per cent. The half-tile start of every second row usually comes from the previous row's offcut, so it costs little extra.
- Diagonal, 45 degrees: 15 per cent. Every perimeter tile is cut, and cut to a triangle. Two triangles rarely make one usable tile.
- Herringbone: 20 per cent. Every edge is an angled cut and the offcuts are all the wrong shape for anywhere else.
These are the figures the tile calculator uses. They are a starting point, not a guarantee — the room decides the rest.
What pushes it higher
- Small rooms: Waste does not scale. A cloakroom is nearly all perimeter, so the proportion of cut tiles is far higher than in a hall of the same layout.
- Big tiles in small spaces: A 600 mm tile in a 2.2 m room means every run ends in a cut, and a cut from a large tile wastes a large piece.
- Irregular shapes: Bay windows, chimney breasts, angled walls. Every extra corner is another cut with an unusable remainder.
- Patterned or directional tiles: If the tile has a grain or a print that must run one way, you cannot rotate an offcut to make it fit.
- Natural stone: Colour and marking vary between pieces, so you will reject some on appearance alone. Twenty per cent is not unreasonable.
What pulls it lower
Large, simple, rectangular rooms with small tiles waste very little. A 6 × 4 m room in 300 mm tiles on a straight grid may genuinely come in under 8 per cent. But the saving is small in absolute terms, and running short is expensive, so the convention holds at 10.
The argument for ordering more than you need
This is the one material where over-ordering is actively sensible, and the reason is batch matching.
Tiles are made in batches, and colour varies between them — sometimes subtly, sometimes not. Two years from now, when a pipe leak means lifting four tiles, the shop will not have your batch. Whatever you patch with will be visibly different.
Keep a box back. A spare box in the loft costs the price of a box; the alternative is retiling a floor because you cannot match four tiles.
Apply it to the order, not the room
The floor is the size it is. Measure the true area, then add waste to the *purchase*, then round up to whole boxes — tiles are sold by the box, not the tile.
That final rounding often supplies a good part of the waste allowance on its own. A room needing 46 tiles, sold 12 to a box, means four boxes and 48 tiles before any waste factor is applied at all.