Quick answer: For straight and brick layouts in a regular room, add 10%. For diagonal (45°) layouts, add 15%. For herringbone, add 20%. If your room has alcoves, niches, or many obstacles, add 5% more to any of these figures.
The waste percentage isn't an arbitrary cushion — it's a direct result of geometry. Every cut tile that can't be reused is waste. How much you waste depends on how many cuts you need (determined by room shape) and what angle those cuts are at (determined by your layout pattern).
Here's a complete breakdown of what waste factor to use and why.
Waste factor by scenario
10%
Straight or brick lay, rectangular room
The standard. Cuts at walls are 90° — offcuts from one wall can often be used on the opposite wall. Breakage and bad cuts account for the rest.
12–13%
Straight lay, irregular room or many obstacles
L-shaped rooms, alcoves, columns, and many door openings all require more cuts, none of which can be reused elsewhere.
15%
Diagonal 45° layout, rectangular room
Every perimeter tile is cut at 45°, producing large triangular offcuts. These triangles are too small to use for other cuts, so all are discarded.
20%
Herringbone pattern, or diagonal in complex room
Herringbone requires cuts at multiple angles. The close-fitting V-pattern means a bad cut wastes the tile entirely — no reusing half-cuts elsewhere.
Waste by tile size
Larger tiles generate more waste per cut. A single bad cut on a 24×24" tile wastes 4 sq ft of tile. The same mistake on a 4×4" tile wastes 0.11 sq ft.
Tile size
Straight lay waste
Diagonal waste
Reason
Mosaic (≤4×4")
8–10%
12–13%
Offcuts are tiny; sheets can be cut precisely
Small (6×6" – 6×12")
10%
13–15%
Standard waste applies
Medium (12×12" – 12×24")
10%
15%
Most common tile size range standard
Large (18×18" – 24×24")
10–12%
15–18%
One bad cut = large waste; harder to handle
Extra large (30"+ / 60cm+)
12–15%
18–20%
Very expensive per tile; requires skilled cutting
Why you should always keep spare tiles
Beyond installation waste, the second reason to buy extra is future repairs. Tiles crack. Heavy objects drop. Floors settle. Grout crumbles and has to be drilled out. When you need to replace a tile in 5 years, you'll need one that matches exactly — same color, same texture, same size, same dye lot.
Tiles are discontinued constantly. A product that's on shelves today may be gone in 18 months. Storing 5–10 spare tiles costs almost nothing and can save you a nightmare repair situation.
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Store spares with lot number
Keep at least 5 spare tiles in the original box with the lot number visible. Store them flat in a dry area. Label the box with the room they came from.
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Check lot numbers before buying
At the store, check every box. Tiles from different lots — even the same product — can differ in shade by as much as a paint chip. Order enough from one lot to finish the job.
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Add rooms, don't deduct openings
When tiling multiple rooms, add the areas together before calculating waste — not separately. Don't subtract doorways or appliance footprints from your total; those cuts still waste tile.
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Waste % before dividing into boxes
Apply your waste percentage to the square footage, then divide by your tile's coverage per box. Don't add waste after calculating boxes — you'll end up short.
The 10% rule means buying 10% more tile than your room's net square footage, to cover waste from cuts, breakage, and fitting. It applies to straight and brick-offset layouts in rectangular rooms. Calculate 10% of your net area and add it before dividing into boxes.
Yes — use at least 15% for diagonal (45°) layouts. Every tile along the perimeter walls must be cut at a 45° angle, producing large triangular offcuts that can't be reused anywhere else. In rooms with alcoves or many corners, use 18–20%.
Budget 20% waste for herringbone. The V-pattern requires complex cuts at multiple angles at every wall edge. Professional tilers sometimes budget 25% for tight herringbone jobs in complex rooms. It's the most cutting-intensive pattern — account for it generously.
Keep at least 5 spare tiles — or one full box, whichever is more — stored with the box, lot number, and room label. This protects you against future repairs. Tiles are discontinued frequently; the chance of finding an exact match in 3–5 years is low unless you kept originals.
Yes, somewhat. Very small tiles (mosaic sheets) can get away with 8% because offcuts are tiny and the mesh sheets can be trimmed precisely. Very large tiles (24×24" or bigger) may need 12% even for straight lay because one bad cut destroys an expensive tile. 10% is correct for the vast majority of standard ceramic and porcelain formats.
Calculate your tiles with the right waste factor
Select your pattern and get the waste auto-applied — then see tiles, boxes, grout, and your full supply list.