How this calculator works
The surface area is divided by the area of one tile, increased by the waste allowance, and rounded up to a whole tile because cut tiles still come from a whole piece. The tile count is then divided by the tiles per box and rounded up again, so the last box may be only partly used. The waste allowance covers cuts at walls, breakage and a spare or two for later repairs.
Formula
A = L × W; n = ceil(A × (1 + waste%) ÷ (tile width × tile length)); boxes = ceil(n ÷ tiles per box). Both areas must use the same unit before dividing.
Worked example
A 10 × 12 ft floor with 12 × 12 in tiles at 10% waste: 120 ft² needs 132 tiles, which is 11 boxes at 12 tiles per box. A 2.4 × 1.2 m wall with 10 × 20 cm subway tiles at 10% waste needs 159 tiles.
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Frequently asked questions
Do grout joints change the tile count?
Slightly. The nominal tile face with a joint is a little larger than the tile itself, so counting the nominal size is close enough for ordering; thin joints under 1/8 in barely move the total.
How much waste should I allow?
About 10% for a straight running lay in a simple room, and 15% for diagonal or herringbone patterns or a room full of corners. Keep one or two spare tiles after the job for repairs.
Why do the tiles and boxes both round up?
You cannot buy part of a tile or part of a box. Rounding separately can leave a few spare tiles, which is preferable to running short when a box is discontinued.