Add every area you're tiling, set the tile size and grout gap, then pick your layout. Diagonal and herringbone eat far more tile than a straight grid, so the waste factor moves with the pattern.
Two things get counted, and they don't give the same answer.
Coverage is the honest one: total floor area × waste factor, divided by the square footage printed on the box. That's what a supplier will quote you.
Piece count divides the area by the footprint of one tile plus its grout gap. A 12 × 24 tile with a 1/8 in gap actually occupies 12.125 × 24.125 in, so it covers about 2.03 ft² rather than 2.00.
A straight grid only wastes tile at the walls. A diagonal layout produces two cut triangles at every edge, and most of those offcuts are unusable. Herringbone is worse again because the cuts are angled and handed. That's the difference between ordering 10% extra and 20% extra — on a 400 ft² floor, about 40 ft² of tile.
Tile is fired in batches and the colour shifts between them. If you crack one in two years and go back for a single box, it will probably not match. Ordering one extra box up front is the cheapest insurance in the whole job.
| Assumption | Value used |
|---|---|
| Waste — straight grid | 10% |
| Waste — brick / running bond | 12% |
| Waste — diagonal | 15% |
| Waste — herringbone / chevron | 20% |
| Grout gap added to both tile dimensions | yes |
| Boxes rounded up to whole cartons | yes |
Waste percentages are starting points used across the trade, not a standard. Coverage per box varies by product — take it off the carton rather than trusting a default.
Only a little, and it works in your favour — the gap means each tile covers slightly more floor. On a small bathroom it's noise. On a large open floor it can save a box.
10% for a straight layout in a simple rectangular room. 15% for diagonal, 20% for herringbone, and add a few points more for rooms with lots of alcoves, doorways or angles.
Yes. Grout gaps like 1/8 or 3/16 work, and room dimensions accept 12' 6 1/2".