How much waste should I allow for tile?

Around 10% for a straight lay in a simple rectangular room, and 15% or more for a diagonal or herringbone layout, where every edge tile is a cut. Complicated outlines with alcoves and doorways push it higher still.

Do I need to allow for grout lines?

Not in the tile count. A grout joint makes each tile cover marginally more than its own size, so ignoring it errs towards buying slightly too many — which is the safe direction.

Why keep the spare tiles?

Because ranges get discontinued and dye lots shift. A single cracked tile three years from now is a repair if you kept spares, and a re-tiled floor if you did not.

Home & construction

Tile Calculator

Enter the area and your tile size to see the tiles needed, the boxes to buy and the spares left over.

The link carries your figures, so it reopens on exactly these numbers.

What each waste allowance adds

Your room, your tiles. The spares column is what you have left over — cut tiles are not spares, and a box you never open is the cheapest insurance on the job.

Waste allowance	Tiles needed	Boxes to buy	Spare tiles left
NoneOnly if every cut is usable, which they never all are.	140	18	4
5%	147	19	5
10%A straight lay in a simple rectangle.	154	20	6
15%Diagonal layouts, or an awkward outline.	161	21	7
20%Patterned tile, or a room full of angles.	168	21	0

The formula

tile area = width × height ÷ 144

tiles = ⌈ area × (1 + waste ÷ 100) ÷ tile area ⌉

boxes = ⌈ tiles ÷ tiles per box ⌉

Worked example

280 ft² of floor in 12 × 24 in tiles, 10% waste, 8 per box

12 × 24 ÷ 144 = 2 ft² per tile
280 × 1.10 = 308 ft² to cover
308 ÷ 2 = 154 tiles
154 ÷ 8 = 19.25 → 20 boxes

Where this goes wrong

Buying the exact number of tiles the area needs

Tiles are sold by the box and cut at every edge, so the arithmetic answer is never the shopping list. A 280 ft² floor needs 154 tiles but 20 boxes — 160 tiles. Ordering 19 boxes leaves you two tiles short with the floor half laid and the range possibly gone.

Questions

How much waste should I allow for tile?: Around 10% for a straight lay in a simple rectangular room, and 15% or more for a diagonal or herringbone layout, where every edge tile is a cut. Complicated outlines with alcoves and doorways push it higher still.
Do I need to allow for grout lines?: Not in the tile count. A grout joint makes each tile cover marginally more than its own size, so ignoring it errs towards buying slightly too many — which is the safe direction.
Why keep the spare tiles?: Because ranges get discontinued and dye lots shift. A single cracked tile three years from now is a repair if you kept spares, and a re-tiled floor if you did not.