Ordering tile short is a project-stopper: dye lots change between batches, so the box you buy next month may not match the floor you laid this month. This calculator counts tiles the way tilers lay them — each tile occupies its size plus one grout gap — then adds your waste allowance and rounds up to full boxes.
The formula
The grout gap matters more than people think. A 12 in tile on a ¼ in gap really covers 12.25 × 12.25 in of floor — about 4% more area per tile than the bare tile size suggests. Ignoring the gap on a big floor under-orders by a box or more.
How much waste should I allow?
10% covers straight grid layouts in rectangular rooms. Use 15% for diagonal layouts, rooms with many corners, or large-format tile (where one bad cut is expensive), and 20% for herringbone and complex patterns. The leftovers are not wasted money: a handful of spare tiles from the same dye lot are the only perfect repair for a future cracked tile.
Grout and thinset
As planning figures: a 25 lb bag of polymer-modified thinset covers roughly 40–50 ft² with a ¼ in trowel (less for large-format tile, which is back-buttered). Grout use varies widely with tile size and gap — small tiles with wide gaps can use five times more grout than large tiles with hairline gaps; check the coverage table on the bag against your tile size and gap before buying.
Worked example
A 100 ft² floor with 12 in × 12 in tiles and a ¼ in grout gap: each tile covers 12.25 in × 12.25 in = 1.042 ft², so the exact count is 100 ÷ 1.042 = 96 tiles. With 10% waste you buy 106 tiles — 11 boxes of 10 — and keep the spares.
How to use this tool
- Measure the area, or type its size directly if you already know it.
- Enter the tile's true width and height and the grout gap you will use.
- Set the waste allowance for your layout pattern.
- Enter tiles per box from the packaging to get the box count.
- Buy the full box count in one trip so every tile shares a dye lot.
Layout tip: start from the centre
Professional tilers snap chalk lines through the centre of the room and lay outward, so cut tiles land symmetrically at the edges instead of a full tile on one wall and a sliver on the other. If your tile count lands just over a whole number of boxes, that is normal — the edge cuts are exactly what the waste allowance is for.