The short answer
Buy about 10% extra tile for a straight layout in a simple room, 15% for a diagonal layout or a room with many corners, and 15 to 20% for herringbone, large-format tiles or natural stone. A 10 × 8 ft floor with 12 × 12 in tile needs 80 tiles; with 10% overage that is 88 tiles, or 9 boxes of 10 sq ft.
Why you need extra tile
Almost every tile along a wall, a doorway or a fixture has to be cut, and the offcut is often too small to use elsewhere. Some tiles crack while cutting or arrive chipped. You also want a few spares for later: tile is made in batches, and a box bought years from now may not match in shade or size.
Overage by layout
| Layout or tile | Overage to add | Why |
|---|---|---|
| Straight grid, simple square room | 10% | Cuts only along the walls |
| Straight grid, many corners or a bathroom with fixtures | 12–15% | More cuts around obstacles |
| Offset or brick pattern | 10–15% | Each row ends with a cut piece |
| Diagonal (45°) | 15% | Every edge tile is cut at an angle |
| Herringbone or chevron | 15–20% | Many small angled cuts |
| Large-format tile (24 in and up) | 15% | One broken tile is a large share of the area |
| Natural stone or handmade tile | 15–20% | More variation and breakage; you may reject pieces |
Flooring Clarity suggests about 10% for ceramic or porcelain tile in a simple layout, 15% for a complex room and 20% for diagonal or patterned layouts. The ranges above follow the same idea: the more angled cuts, the more extra you need.
How to calculate tile with overage
Floor area = length × width
Tiles = floor area ÷ (tile length × tile width ÷ 144) × (1 + overage %), rounded up
Boxes = tiles × tile area ÷ coverage per box, rounded up
- Floor area: 10 × 8 = 80 sq ft.
- One 12 × 12 in tile covers 1 sq ft, so the floor needs 80 tiles before overage.
- Add 10%: 80 × 1.10 = 88 tiles.
- At 10 sq ft per box: 88 ÷ 10 = 8.8, so buy 9 boxes.
- For a diagonal layout at 15%: 80 × 1.15 = 92 tiles, or 10 boxes.
Examples by tile size
| Project | Overage | Tiles | Boxes |
|---|---|---|---|
| 10 × 8 ft floor, 12 × 12 in tile, 10 sq ft boxes | 10% | 88 | 9 |
| Same floor laid diagonally | 15% | 92 | 10 |
| 10 × 8 ft floor, 12 × 24 in tile, 8 sq ft boxes | 10% | 44 | 11 |
| 12 × 10 ft floor, 18 × 18 in tile, 13.5 sq ft boxes | 10% | 59 | 10 |
| 5 × 8 ft shower wall, 3 × 6 in subway tile, 12.5 sq ft boxes | 15% | 368 | 4 |
The tile calculator does the same steps for any room and tile size, and has presets for 5%, 10% and 15% overage.
Buying tips
- Check that every box has the same lot or batch number before you leave the store.
- Keep at least a few spare tiles after the job, stored flat in a dry place, for future repairs.
- Ask about the return policy for unopened boxes; many stores accept them, which makes rounding up low risk.
- Trim pieces such as bullnose, edge or cove tile are counted by the linear foot, not by area.
Calculators for this job
These calculators do the arithmetic from this guide. Each card shows the result for a typical project; open one to enter your own measurements.
Frequently asked questions
Is 10% extra tile enough?
For a straight grid in a simple, square room, yes. Add more for diagonal or herringbone layouts, rooms with many corners, large-format tiles and natural stone.
How much extra tile for a diagonal layout?
About 15%. Every tile along the walls is cut at an angle, and the triangular offcuts are rarely reusable.
How much extra tile for herringbone?
Plan on 15 to 20%. Herringbone has many angled cuts along every edge, and small rectangular tiles break more easily while cutting.
How many spare tiles should I keep after the job?
Keep at least a few tiles, or a full box for a large floor. A matching replacement is often impossible to find later.
Sources
- Flooring Clarity, How Much Extra Tile to Buy for a Project
- Flooring Clarity, How Much Extra Flooring To Buy