Tile calculator
Ten per cent covers a straight grid in a square room. A diagonal lay wastes far more at the edges; allow twenty. A patterned or rectified tile that has to line up across a doorway wants fifteen. And whatever the number says, buy from one batch: tile colour shifts between batches, and the box you go back for in a month will not match.
Divide the area by the area of one tile, then add for cuts and breakages. A 4 × 3 m floor is 12 m² and a 30 × 30 cm tile covers 0.09 m², so the bare count is 133.3 tiles; a 10% allowance rounds that up to 147.
How to count tiles
The waste allowance does more work than its name suggests. Part of it is genuine offcut: every tile meeting a wall gets cut, and on a straight lay the piece left over is the wrong shape for anywhere else. Part is breakage, in transit and on the wet saw, and the first few cuts of a job break more than the last few. The rest is insurance against shade. Ceramic and porcelain are fired in runs, colour drifts between runs, and every box carries a batch or shade code for that reason. A box bought a month later is a gamble, and a mismatched last row is a re-tile rather than a repair.
Layout is what moves the allowance, not room size. A straight grid wastes the least, because every cut row runs along one wall. A diagonal lay cuts two triangles from every perimeter tile and leaves scrap at four edges instead of two. Herringbone is worse again, since the offcuts are angled and rarely reusable. An offset or brick bond sits in between, and any tile with direction in the pattern loses whatever does not line up.
The count here treats the floor as pure area, which is the assumption to be aware of. It does not know where your cut line falls, and a room 3.05 m wide across a 30 cm tile needs the same number of rows as one 3.29 m wide, with a very different sliver at the edge. Setting out from the centre so both edges take an equal cut is standard practice and looks far better than starting tight against one wall and finishing with a 20 mm strip. It costs nothing in tiles and it is the single decision that separates a tidy floor from an obvious one.
Grout joints work in your favour and are usually ignored on purpose. Adding a 3 mm joint to a 30 cm tile makes the repeating module 303 mm, so a square metre takes 10.9 tiles instead of 11.1, about 2% fewer. That sits well inside the waste allowance, so leaving it out simply makes the estimate slightly generous. Wide joints on rustic or handmade tiles are the exception: at 8 or 10 mm the effect is large enough to be worth adding the joint to each tile dimension before you enter it.
What people use it for
- Ordering tiles for a bathroom or kitchen floor
- Working out a splashback or a shower enclosure
- Comparing a large-format tile against a small one for the same room
- Costing a herringbone or diagonal lay against a straight one
- Converting between square metres and box counts
- Checking a tiler’s materials quote against your own measurements
- Working out how many spare tiles to keep after the job
Questions
Ten per cent for a straight lay in a simple rectangular room, fifteen for a room with alcoves or a patterned tile, twenty for a diagonal or herringbone lay, and more again on a room full of pipe boxings.
Eleven and one ninth, so twelve in practice. A 60 × 60 is 2.78 per square metre, a 20 × 20 is 25, and a 10 × 10 mosaic chip is a hundred.
Up to about 5 mm, no. A 3 mm joint on a 30 cm tile reduces the count by roughly 2%, which the waste allowance already covers. Above 5 mm, add the joint to each tile dimension before entering it.
Because boxes round up independently. At 147 tiles and twelve to a box that is thirteen boxes, or 156 tiles. The extras are the spares you should be keeping anyway.
Around 4 kg per square metre for floor tiles at a 6 mm notch, and roughly half again at a 10 mm notch. Large-format tiles are back-buttered as well as bedded, which can double it.
A rectified tile is machine-cut to size after firing, so its edges are square and it will take a 2 mm joint. A pressed tile shrinks unpredictably in the kiln and varies by a millimetre or two, which needs a 3 mm joint or more to absorb.
Yes, and keep it somewhere dry with the batch number on it. A cracked tile in three years is a five-minute repair with a matching spare and a very visible one without.
Rarely, and it does not have to. Nominal sizes are trade names: 60 × 60 is commonly 597 × 597 and 30 × 60 is often 298 × 598. Measure one before you calculate anything tight.
Set out so the cuts land at the edges you see least, and split them evenly between opposite walls rather than leaving one full row and one sliver. In a bathroom, keep the full tiles where the eye lands as you walk in.
Three hundred and thirty at a 10% allowance. Small tiles cost more in labour than in material, since the number of cuts, the grout length and the time all rise as the tile shrinks.
Per tile. Enter the price of one tile and it multiplies by the tile count, so a price taken off a per-square-metre label needs converting first.