Tile Waste Factor: How Much Extra Tile to Buy
Every guide tells you to add 10 to 15 percent. That figure describes the tile you cut and throw away — not the tile you end up paying for, which is decided by the box.
Waste factor by layout pattern
Planning figures used across the trade, and the same ones our calculators apply. They are conventions, not standards — no code sets them.
| Layout | Waste factor | Why it lands there |
|---|---|---|
| Straight / stacked grid | 10% | Cuts only at the perimeter, and offcuts from one wall often serve the opposite one |
| Offset / running bond | 12% | Every course starts with a part tile, and the offcut is not always reusable |
| Diagonal (45°) | 15% | Every perimeter tile is cut, and a triangular offcut rarely fits anywhere else |
| Herringbone or chevron | 20% | Two cuts per perimeter piece and a layout that punishes mistakes |
Waste factor by job, because cuts follow edges
Waste tracks the density of cut edges, not the floor area. A small room with a lot of obstacles wastes more than a big empty one.
| Job | Start from | What is driving it |
|---|---|---|
| Large open floor, straight layout | 10% | The best case: a high ratio of field tile to perimeter |
| Floor with cabinets, islands or a hearth | 12–15% | Every obstacle is another run of cut edges |
| Small bathroom floor | 15% | Almost all perimeter, hardly any field |
| Kitchen backsplash | 15% | Outlets, the range gap and two finished ends |
| Shower walls and pan | 15–20% | Three internal corners, a curb, a niche, a valve and a sloped floor |
| Any job with a mitred edge or a border | add 5% | Mitres are cut twice and broken often |
⭐ What you actually pay for: the box rounds everything up
A 15.5 sq ft box, 10% waste factor, rounded up to whole boxes. The right-hand column is the overage you really buy — and note that it is lumpy, not a smooth curve.
| Area to tile | Area + 10% | Boxes you must buy | Tile you take home | Overage you actually pay for |
|---|---|---|---|---|
| 20 sq ft | 22.0 | 2 | 31.0 sq ft | 55% |
| 50 sq ft | 55.0 | 4 | 62.0 sq ft | 24% |
| 80 sq ft | 88.0 | 6 | 93.0 sq ft | 16% |
| 100 sq ft | 110.0 | 8 | 124.0 sq ft | 24% |
| 200 sq ft | 220.0 | 15 | 232.5 sq ft | 16% |
| 400 sq ft | 440.0 | 29 | 449.5 sq ft | 12% |
Attic stock: what to keep on purpose
Leftover tile is not waste if you keep it. Discontinued lines and dye-lot drift make a future repair almost impossible to match.
| Situation | Keep |
|---|---|
| Standard floor or wall | At least one full box |
| Discontinued or clearance tile | Two boxes — there is no second chance |
| Handmade or small-batch tile | Two boxes, from the same run |
| Rental or commercial floor | Two boxes, labelled and stored on site |
The number everyone quotes answers the wrong question
Ask how much extra tile to buy and you will be told 10 to 15 percent, everywhere, without much variation.
That figure is not wrong. It is answering a different question from the one you asked. It describes the tile that gets cut and thrown away — the offcuts, the mis-cuts, the piece that snapped on the wet saw. It is a property of the layout and the installer.
What you asked was how much tile to buy. And you cannot buy 10 percent. You buy boxes.
Those two numbers are close on a big job and wildly different on a small one, which is what the third table above is for and what most waste guides skip entirely.
Waste follows cut edges, not floor area
Both the pattern table and the job table are really measuring the same thing from two directions: how much of your tile meets an edge.
A field tile in the middle of a room is laid whole. A tile at the perimeter is cut, and the offcut is only useful if some other edge happens to need that exact piece. So waste is driven by the ratio of perimeter to field, and by how awkward the cuts are.
That explains results that otherwise look inconsistent:
- A large open floor is mostly field tile. 10 percent covers it.
- A small bathroom is almost all perimeter. The same 10 percent does not.
- A diagonal layout turns every perimeter tile into a triangle, and triangular offcuts almost never pair up.
- A shower is the worst case in the house: three internal corners, a curb, a niche, a valve, a shower arm and a floor that slopes to a drain. Nearly every tile in it meets something.
Take the higher of the two tables rather than averaging them, then add for mitres or borders if you have them.
The part the charts leave out
Here is the arithmetic nobody puts in front of you.
Tile is sold in boxes, and a box is typically around 15.5 square feet for 12 × 24 porcelain. You cannot buy two thirds of one. So whatever percentage you add, the order gets rounded up to a whole box — and on a small job that rounding dwarfs the waste factor you so carefully chose.
A 20 square foot bathroom floor plus 10 percent is 22 square feet. That is two boxes, which is 31 square feet. You just bought 55 percent extra, not 10.
And the effect is not a smooth curve that fades as the job grows. It is lumpy, because what matters is where your area happens to land relative to the box size:
- 80 square feet plus 10 percent needs 6 boxes and lands you 16 percent over.
- 100 square feet plus 10 percent spills just past 7 boxes, so you buy 8 and land 24 percent over.
The bigger floor wastes proportionally more. Nothing about the job changed — only the rounding.
Two practical consequences follow.
On a small job, stop agonising over the percentage. Below roughly 50 square feet the choice between 10 and 15 percent usually does not change the box count at all. Work out the boxes, and if you are within a tile or two of the next one, buy it.
On a big job, it is worth checking the landing. If your order lands barely over a box boundary, a slightly different tile size — or a supplier whose boxes hold a different area — can save a real amount of money. Recompute with the coverage printed on the carton in front of you, because 15.5 is a common figure, not a rule.
Leftovers are not waste if you keep them
The last table reframes the whole question, and it is the part experienced tilers care most about.
Tile is fired in batches, and colour drifts between them. The batch — the dye lot — is printed on the carton. Two boxes of nominally identical tile from different lots can be visibly different laid side by side, and you will notice it forever.
This has two consequences:
Buy the entire job in one purchase. Not most of it now and the rest next week. One purchase, one lot, no surprises. This is also the practical argument for erring high: coming back for one more box is exactly how you end up with a mismatched patch in the middle of a floor.
Keep a box. Deliberately. A cracked tile in three years is a twenty minute repair if you have matching stock and a serious problem if you do not, because the line may be discontinued and the lot certainly will be. On a discontinued or handmade tile, keep two.
Stored flat, somewhere dry, labelled with the room. It is the cheapest insurance in the whole project, and it is why "waste" is the wrong word for the last box.
Putting it together
The order of operations that actually works:
- Measure your net area — the surface minus anything you are not tiling.
- Pick the pattern factor from the first table.
- Check the job table and take the higher of the two.
- Convert to boxes, using the coverage printed on your carton, and round up.
- Look at the result. If you are close to the next box, take it.
- Keep at least one box back as attic stock.
Steps 1 to 4 are what the tile calculator does, and it applies the pattern factor for you. If you are tiling a shower — the case where all of this bites hardest — the shower tile calculator adds up the walls, pan, curb and niche separately, because that is where the cut edges hide.
And once you know how much tile you are buying, the grout joint width chart decides how much grout goes between it.
Common questions
Is 10% enough?
For a large, open, straight-laid floor with a competent installer, usually yes. For anything smaller or more cut-up it is optimistic, and for a shower or a herringbone floor it is simply wrong. Use the pattern table and the job table together, take the higher of the two, and then check what the box arithmetic does to it.
Why does a 100 sq ft floor waste more than an 80 sq ft one?
Because of where each one lands relative to the box. At 15.5 sq ft per box, 80 sq ft plus 10% needs 6 boxes and you end up 16% over. 100 sq ft plus 10% spills just past 7 boxes, so you buy 8 and end up 24% over. Nothing about the job changed — only the arithmetic of rounding up. It is worth checking whether a slightly different tile size or box count lands better before you order.
Should I buy the extra box even if the calculator says I don't need it?
On a small job, yes, and the box table is the reason. Below about 50 square feet a 10% allowance is often less than a single tile's worth of insurance, and running one tile short means a second trip, a possible dye-lot mismatch, and a job stopped in the middle. The marginal box is the cheapest insurance on the whole project.
What is a dye lot and why does it matter here?
Tile is fired in batches and the colour drifts between them, sometimes subtly and sometimes not. The batch is printed on the carton. Buy the whole job in one purchase so every box shares a lot, and keep your leftovers from that same lot — a repair tile from a different batch can be visible across a room.
Where these numbers come from
- The pattern and job figures are the allowances commonly specified by tile setters and echoed in the TCNA Handbook's guidance on layout and cut waste. They are planning figures, not a warranty, and no code sets them.
- The box-rounding table is plain arithmetic at 15.5 sq ft per box, which is a common figure for 12×24 porcelain. Your box coverage is printed on the carton and varies by product and production run — recompute with your own figure.
- Dye-lot and attic-stock advice is standard industry practice rather than a published standard.
Last checked 2026-08-17.