Tile waste: should you add 10% or 15%?

Every tile job loses some tiles. Some are cut and the offcut is too small to use, some break, some have a chip you only notice after opening the box. The question is not whether to buy extra, but how much. “Add 10%” is the rule of thumb everyone repeats, and for many rooms it is fine. For others it is not enough. Here is how to decide.

Why tile gets wasted

Waste comes from three places:

1. Cuts at the edges. Every row that meets a wall needs a cut tile. The more walls, corners and obstacles a room has, the more cuts.
2. Layout pattern. Patterns that run at an angle to the walls, such as diagonal and herringbone, create a cut at the end of almost every row, and many of those offcuts cannot be reused.
3. Breakage and defects. A few tiles crack during cutting or arrive damaged. Large and thin tiles are more fragile.

Typical allowances

These are common starting points, not rules. Adjust them for your room and your experience.

Situation	Extra to buy
Straight lay, simple rectangular room	about 10%
Straight lay with many corners, cabinets or pipes	10–15%
Diagonal layout	about 15%
Herringbone or chevron	15–20%
Large-format tiles (60 cm / 24 in and up)	add a few percent more

If you are new to tiling, lean towards the higher end. A spare box costs less than a second trip, and a second batch may not match.

Worked example: a 12 × 10 ft kitchen floor

1. Area: 12 × 10 = 120 square feet.
2. Remove what will not be tiled. A kitchen island that sits on the subfloor, 6 × 3 ft, takes away 18 ft². Tiled area: 102 ft².
3. Add waste. The room has a few corners and the tiles go in a straight lay, so 10%: 102 × 1.10 = 112.2 ft².
4. Convert to boxes. Suppose the tile is 12 × 24 inches (2 ft² each) and comes 8 to a box, so one box covers 16 ft². 112.2 ÷ 16 = 7.01, which rounds up to 8 boxes.

Notice how much rounding up matters. The waste allowance gave us 112 ft²; eight boxes give us 128 ft². That leftover is useful, which brings us to the next point.

Keep a few tiles for later

Tiles are made in batches, and colour and size can vary slightly between them (the batch is often marked on the box as a “lot” or “shade” number). If a tile cracks in five years, the same product may be discontinued or come from a batch that looks different. Keeping a handful of spare tiles from the original purchase makes repairs invisible. When you buy, check that all boxes have the same lot number.

Metric example: a 2.4 × 1.8 m bathroom

1. Area: 2.4 × 1.8 = 4.32 m².
2. The bath covers 1.7 × 0.75 = 1.28 m², leaving 3.04 m².
3. Diagonal layout, so 15%: 3.04 × 1.15 = 3.50 m².
4. A box covers 1.44 m²: 3.50 ÷ 1.44 = 2.43, so 3 boxes.

Don’t forget the rest

• Grout and adhesive are calculated from area too. Manufacturers give coverage per bag for a given tile size and trowel notch.
• Skirting or wall tiles are separate. Measure the perimeter for skirting and wall area for walls, and treat them as their own estimate.
• Trim pieces for edges and corners are sold by the piece. Count them, don’t estimate them from area.

The BuildCalc tile calculator takes your room size, tile size and waste percentage, and tells you how many tiles and boxes to buy.