How Much Extra Tile Should You Buy?
Allowance by layout
| Layout | Add | Reason |
|---|---|---|
| Straight lay, rectangular room | 10% | Cuts on two edges only |
| Straight lay, many corners, niches, closets | 12–15% | Each obstruction creates part-tiles |
| Diagonal / 45° | 15% | Every perimeter tile becomes a triangle |
| Herringbone, chevron, basketweave | 20% | Two cuts on most edge tiles |
| Large format, 24 in and over | 10–15% | Fewer cuts, but each breakage is expensive |
| Mosaic sheets | 10% | Sheets can be cut between tiles |
What the allowance is actually for
Three separate things get lumped into "waste", and they behave differently:
- Cuts. A tile cut to fit a perimeter leaves an offcut that usually cannot be used elsewhere, because the next gap is a different width. This is the dominant cost and it scales with the perimeter, not the area — which is why small rooms need a bigger percentage than large ones.
- Breakage. Snapped tiles during cutting, chipped edges, a dropped box. Higher with thin large-format porcelain and with brittle natural stone.
- Rejects. Natural stone and hand-made tile vary in shade; you will set some aside. Budget extra for anything marketed as "variation: high".
Box rounding often pays for the allowance
Tile is sold in whole boxes, and that rounding frequently delivers most of the allowance for free. From the worked example in the calculator: a 120 sq ft floor in 12 × 24 in tile needs 60 tiles bare, 65 with a 10% allowance — but at 8 tiles to a box you buy 9 boxes, which is 72 tiles. The box rounding alone gave you 20%.
The lesson is to compute the tile count first and the boxes second, and not to pile a large percentage on top of a rounding that has already covered you. Where it goes the other way — 8 boxes exactly, zero spare — that is the moment to add one more box deliberately.
When to buy a whole extra box regardless
- Clearance or discontinued lines. There is no second trip. Buy the tile you might need.
- Dye-lot sensitive product. Production runs shift in shade. A replacement bought in two years will not match, and on a floor a single mismatched tile is obvious.
- Floors in wet areas or over slabs. A future plumbing repair or slab crack means lifting tiles. Having originals turns a re-tiling job into a patch.
- Anything shipped from far away. Freight on one replacement box costs more than the box.
What not to include in the measurement
Do not tile under base cabinets that are staying — it is money on the floor and it can raise the appliance opening. Do tile under a freestanding range or dishwasher, because those get pulled out, and an untiled hole under a replaced appliance is both visible and a snagging point.
Deduct fixed obstructions bigger than a few square feet, such as a kitchen island footprint or a built-in tub, but leave small deductions in place as part of the allowance.
Storing what is left
Keep spares flat, dry and inside — not stacked on edge in an unheated garage where freeze-thaw and knocks will chip them. Write the room and the dye lot on the box. It is the cheapest insurance in the whole job.
Enter the area and your tile size to get the tile count, the number of boxes to buy, and the square footage to quote — with the grout joint and a cut allowance included, which is where most tile estimates go wrong.
Frequently asked questions
Is 10% enough extra tile?
For a straight layout in a rectangular room, yes. Increase it to 15% for diagonal layouts or rooms with many corners and closets, and 20% for herringbone and chevron patterns where most edge tiles need two cuts.
Do I add the waste allowance before or after rounding to boxes?
Before. Work out the tile count including the allowance, then round that up to whole boxes. Check the result, because box rounding often supplies a good part of the allowance by itself.
Why does tile from the same product not match?
Ceramic and porcelain are fired in batches called dye lots, and colour shifts slightly between production runs. Boxes bought together normally share a lot; a box bought a year later usually does not.
- How to Plan a Tile Layout Before You Start
- How Much Thinset Do I Need?
- How Much Grout Do I Need?
- Can You Tile Over Existing Tile?