How Much Extra Tile Should You Buy?

Cutting loss

Every tile cut to meet a wall, a doorway or a pipe leaves an offcut. Sometimes the offcut is usable at the opposite edge; often it isn't the right size and is thrown away. This scales with how much perimeter and how many obstacles the room has relative to its area — which is why a small bathroom full of fixtures wastes a far higher proportion than a large open floor.

Layout and pattern loss

Where the layout starts and which way it runs decide how many tiles meet a wall part-way and what shape those offcuts are. A grid squared up to the walls tends to produce straight cuts, some of which can be reused at the opposite edge; a diagonal, herringbone, patterned or mosaic layout tends to produce more cuts and more awkward shapes with no second use. A pattern that has to repeat may also force you to discard otherwise good pieces to keep the run aligned. Where you set the starting line changes all of this, so it's worth planning the layout before settling on a figure.

Breakage and defects

Tiles break on the cutter, get dropped, and occasionally arrive chipped or out of tolerance. This is a small allowance on a forgiving tile and a real one on large-format, thin or natural stone pieces, which are more fragile to handle and to cut.

Spares for later

Tile held back deliberately so a cracked tile can be replaced in five years with a piece that matches. This one is different from the other three: it isn't consumed during the job, and it's the part people skip and later regret, because the same tile is often unavailable or a visibly different batch by then.

The first three are consumed while tiling. The fourth is a decision about the future, and it's worth deciding separately rather than hoping the percentage happens to leave enough behind.

Check the box: where the tile manufacturer or your retailer states an overage figure for a specific product or layout, use theirs over any general rule. They know the tolerances, the caliber and the breakage rate of that particular tile.

You buy whole boxes, not tiles

Tile is generally sold by the box, so your order rounds up to a whole box whatever the percentage says. That rounding is itself a source of spare tile — often enough to cover your spares on a small job, occasionally almost nothing if you land just over a box boundary. Work out the box count before deciding whether you need to add anything on top.

Batches don't match

Tile is produced in runs, and colour, shade and size tolerance can shift between them. A second order placed weeks later may be a different batch and visibly different on the floor, even with the same product code. Boxes are usually marked with shade and caliber codes — worth checking that yours match, and worth opening them to compare before the first tile goes down. This is the main practical reason to buy the whole job at once rather than topping up later.

Returns have conditions

Buying generously is only cheap if you can return the surplus. Policies differ on unopened boxes, special orders, time limits and restocking fees, and special-order tile is frequently non-returnable. Check the terms before you decide how much cushion to buy, and keep the boxes you might return unopened and undamaged.

The useful part is the last line. The allowance was 12 tiles, but rounding to whole boxes put 20 beyond the field — the cuts and breakage come out of those 20 first, and whatever is still whole at the end is what you keep. On a job this size that cushion is usually enough to leave a few spares without adding another box.

It can fall the other way, though. A 127 sq ft field of the same tile needs 139.7 tiles with the same 10% — that's 13.97 boxes, so you still buy 14. Those 140 tiles are 13 more than the 127 the floor needs, about 10.24%, but rounding up to the whole box only added 0.3 of a tile on top of the allowance you had already chosen. The cuts and any breakage draw down those 13 as the job goes, so what survives to go in the cupboard is some part of them, not all 13. Identical percentage, identical box count, and much less left over than the first job.

That's the habit worth taking away: run the numbers, look at what the rounding leaves you, and then decide whether the spares you want are already covered.