How Many Tiles Do I Need? Waste, Boxes & Grout Explained

To work out how many tiles you need, divide the area you are tiling by the area of one tile, then add extra for cuts and breakage. The extra is called the waste allowance, and it is usually 10% for a simple straight layout and 15–20% for diagonal or herringbone patterns. Then round up to whole boxes.

The formula

1. Area = length × width, in square feet. For an irregular space, split it into rectangles and add them.
2. Tile area = (tile width in inches ÷ 12) × (tile length in inches ÷ 12). A 12 by 12 inch tile is 1 square foot; a 6 by 6 inch tile is 0.25 square feet.
3. Tiles needed = (area ÷ tile area) × (1 + waste allowance), rounded up.

Example: an 80 square foot floor

Say you are tiling a 10 by 8 foot room, which is 80 square feet. With a 15% waste allowance, here is what different tile sizes require:

For the 12 by 12 inch tile, the waste allowance changes the count like this:

Tile counts are always rounded up to whole tiles, and box counts to whole boxes.

Why waste matters

Tiles get cut around walls, fixtures, and corners, and some break or are unusable. Straight layouts waste the least. Diagonal and herringbone layouts require more angled cuts, so more material is thrown away. Smaller rooms with many corners and obstacles need more waste than large open floors. If you are a first-time DIY tiler, lean toward the higher end.

Converting tiles to boxes

Tile is sold by the box, and coverage per box varies by product. Our calculator uses a rough estimate of 8 to 15 square feet per box depending on tile size, but the number printed on the actual box is the one that matters. Divide your total square footage, including waste, by the coverage per box and round up to the next full box.

Buy a spare box

Add one extra box beyond your estimate if you can. Tile dye lots change between production runs, so a tile bought a year later may not match exactly. A spare box also covers a future repair after a cracked tile or plumbing leak. Keep it in a dry place, and check that all boxes you buy up front share the same lot number.

Estimating grout

Grout use depends on tile size, tile thickness, and the width of the joint. Smaller tiles have more joints and use more grout per square foot than large tiles. Our calculator uses a rough figure of about 1 pound per 40 square feet as a starting point. It is only an estimate; check the coverage chart from your grout manufacturer, which lists coverage by tile size and joint width, and buy accordingly.

Before you order

• Measure twice, and measure the actual tiled surfaces, not the room outline.
• Decide the layout first, since it changes the waste allowance. A tile layout that is centered on the room rather than started at one wall can also change how many cuts you need.
• Confirm the tile is suitable for the location. Floor tile and wall tile are rated differently, and tile for showers and wet areas needs a suitable rating.
• Check that the surface is flat. Large-format tiles are less forgiving of uneven floors.