How much extra tile to buy
By Michał Białas · Last updated
Plan on about 10% extra for a straight or offset layout, 15% for diagonal and 18% for herringbone. Add 5% more in rooms under about 43 sq ft (4 m²), where almost every tile gets cut, and 3% more for tile with an edge of 48 in (1200 mm) or longer, which breaks more easily.
Where tile waste comes from
Tile waste is mostly cut pieces that can’t be used anywhere else. Every row that meets a wall ends in a cut tile, and every cut around a door casing, pipe or floor vent leaves an offcut. A few tiles break, a few arrive chipped, and some get set aside because of shade differences. The more cuts a layout needs, the more tile you buy for the same floor.
Grout joints work the other way. A 12 × 24 in tile with a 1/8 in joint covers a 12 1/8 × 24 1/8 in patch of floor, so slightly fewer tiles are needed than the bare tile area suggests. The tile calculator counts each tile together with one joint before adding waste.
Default waste by layout
| Layout | Waste | Why |
|---|---|---|
| Straight (grid) | 10% | One cut per row at each wall; offcuts often start the next row |
| Offset 1/2 or 1/3 (brick) | 10% | Similar cut count; offsets reuse half tiles |
| Diagonal 45° | 15% | Every edge tile is a triangle cut |
| Herringbone | 18% | Angled cuts at every wall and more breakage |
| Room under 43 sq ft (4 m²) | +5% | Nearly every tile is cut |
| Any tile edge 48 in (1200 mm) or longer | +3% | Long tiles break more easily |
These are starting points, not rules. A simple rectangular room with a tile that divides evenly into it needs less; a room with columns, angled walls and lots of doorways needs more. Every value is editable in the calculator, and the “i” next to the tile line shows which surcharges were applied.
Why boxes change the answer
Tile is sold by the box, so the real question is how many boxes. Rounding up to whole boxes often adds more than the waste allowance itself, which is why switching from straight to herringbone sometimes costs nothing extra in a given room and sometimes costs a whole box.
Example 1 (feet): 12 × 10 ft room, 12 × 24 in tile, 8 per box
- Area 120 sq ft. With a 1/16 in joint (rectified tile), each tile covers 12 1/16 × 24 1/16 in: 120 sq ft ÷ 2.01 sq ft = 59.5 tiles net.
- Straight, 10%: 59.5 × 1.10 = 65.5 → 66 tiles → 9 boxes (72 tiles).
- Diagonal, 15%: 59.5 × 1.15 = 68.5 → 69 tiles → still 9 boxes.
- Herringbone, 18%: 59.5 × 1.18 = 70.2 → 71 tiles → still 9 boxes, with 1 tile to spare.
- Here the box rounding already covers the extra cuts. One more foot of room length would push herringbone to 10 boxes.
Example 2 (meters): small bathroom 2.0 × 1.8 m, 300 × 600 mm tile, 8 per box
- Area 3.60 m², under 4 m², so the small-room surcharge applies: 10% + 5% = 15%.
- Each tile covers 302 × 602 mm with a 2 mm joint: 3.6 m² ÷ 0.1818 m² = 19.8 tiles net.
- With 15%: 19.8 × 1.15 = 22.8 → 23 tiles → 3 boxes (24 tiles).
- Leftover: 24 − 19.8 = 4.2 tiles. Keep them: small bathrooms are where a cracked tile gets replaced years later.
When to buy a spare box
Tile is made in batches, and the shade and sometimes the exact size vary from batch to batch. Many installers keep one spare box from the same batch for repairs, and it is worth doing for any floor you plan to keep for years. Check that all boxes carry the same shade and caliber code before you start, not after half the floor is set.
The calculator’s “keep a spare box” option adds exactly one box on top of the rounded count, so you can see what the spare costs.
Getting a precise count for rectangular rooms
For a rectangular room with a straight or offset layout, the precise count (grid method) counts actual columns and rows and checks the cut pieces at the edges. If a cut piece is half a tile or less and the pattern isn’t directional, two cuts come out of one tile. It adds 3% for breakage and the calculator uses whichever result is larger, the area method or the grid.
- Measure the room carefully (see how to measure a room for flooring).
- Choose the layout and let the waste default fill in, then adjust it for awkward rooms.
- Enter the box contents in pieces or square feet; the calculator warns if they don’t match the tile size.
- Switch on the precise count for simple rectangles.
- Decide on a spare box, then check the shade and caliber codes when the tile arrives.
Common mistakes
| Mistake | Result |
|---|---|
| Ordering exactly the floor area | Short on the last row; the reorder may be a different batch |
| Using 10% for a herringbone floor | Typically short by a box or more |
| Ignoring the joint width with mosaic | Ordering about 6% too much on small tile with wide joints |
| Mixing batches | Visible shade change across the floor |
| Returning every leftover tile | Nothing to repair cracks with later |
Large tiles bring their own waste issues — lippage, leveling clips and breakage. See large-format tile for those.
Frequently asked questions
Is 10% extra tile enough?
For a straight or offset layout in a normal room, usually yes. Use 15% for diagonal, about 18% for herringbone, and add 5% in very small rooms.
Can I return unopened boxes?
Many stores accept unopened boxes, but policies differ, and special-order tile often can’t be returned. Ask before you buy, and keep one box for repairs anyway.
Does the grout joint reduce the number of tiles?
Slightly. Each tile covers its own size plus one joint. The effect is small for large tile and noticeable for mosaic with wide joints.
Why does the calculator show more tiles left over than my waste percentage?
Because tile is sold in whole boxes. The leftover is the box rounding plus the waste allowance minus what the floor actually needs.