Tile Calculator

Five square metres of floor, 12 by 12 inch ceramic, 3 mm joints, laid straight, with a 10% waste factor. The calculator returns 60 tiles, 5 boxes, 1.4 kg of grout, one bag of thin-set and 9 metres of edge trim.

A "12x12" tile is 305 by 305 mm, which is 0.0929 m². Five square metres divided by that is 53.8 tiles, and the 10% waste takes it to 60. The boxes line is the one that matters at the counter: at 12 tiles a box you buy 5 boxes, which is exactly 60 tiles. Tiles are not sold loose, so the number you pay for is always a multiple of the box.

Grout is worked out as a volume rather than guessed. Five square metres of 305 mm tiles contains 32.8 metres of joint; multiply by 3 mm wide and 8 mm deep and weigh it, and you get 1.4 kg. That is why a mosaic floor of the same area needs far more grout than a large-format one — there is simply more joint in it.

Three metres long by 600 mm high is only 1.8 m², but a subway tile is 152 by 76 mm, so that small area takes 155 tiles before waste and 171 after. At 12 to a box that is 15 boxes — 180 tiles in the van for under two square metres of wall.

Small formats are where the box rounding bites hardest. You are buying nine more tiles than you need because the last box cannot be split, and on a run this size that is most of a box of spares. Which is not a bad thing: keep them, because the batch will have changed by the time one cracks.

Five by four metres, 20 m², in 24 by 24 inch porcelain: 60 tiles, 5 boxes, 2.8 kg of grout — and 5 bags of thin-set.

That thin-set figure is the one people get wrong. Coverage follows the tile's longest side, because a bigger tile needs a deeper notched trowel and a deeper notch spreads less per bag. The splashback above got 8 m² from a bag; this floor gets 4. Twenty square metres of large format therefore needs five bags where the same area of small tile would need three.

Two metres by 1.5, just 3 m². In 2 by 2 inch mosaic that is 1,279 tiles and 5.1 kg of grout.

Put that beside the living room: 3 m² of mosaic needs nearly twice the grout of 20 m² of large-format porcelain. There is simply far more joint per square metre when the tiles are 51 mm across, and grout is worked out from the length of joint rather than guessed per tile, which is why the two answers differ so sharply.

One practical note: mosaic is sold on mesh sheets, not loose, so set Tiles per Box to the number of chips on a sheet if you want the box count to mean anything.

Using one waste factor for every layout. A straight grid wastes about 10% because only the perimeter needs cutting. Turn the same floor 45 degrees and every tile at every wall becomes a cut, and the figure climbs. Herringbone is higher again.

The Layout Pattern dropdown tells you what is typical for the pattern you picked, and it never overwrites the waste factor you typed — the advice is there to be taken or ignored, not applied behind your back. The second mistake is ordering the exact count with no allowance at all, which leaves you with no spares for a cracked tile in two years, by which time the batch will have changed shade.

Boxes, not tiles, and the batch matters. Ask for all boxes from the same batch number: ceramic and porcelain shade-vary between production runs, and a floor laid from two batches can show a visible line across it.

Thin-set coverage follows the tile's longest side, because bigger tiles need a deeper notched trowel and a deeper notch spreads less per bag. A 24×12 plank is treated as a 24, not a 12 — the long side is what sets the trowel. Stone is usually back-buttered as well, which uses more again.

The working names the actual tile size in millimetres, so you can check it against the box. Nominal tile names are approximate: a "12x12" is 305 mm because it is a converted 12 inches, and a "600x600" really is 600. If your tile is a genuine 300 mm, use the Custom size option rather than the nearest named one — over a large floor the difference is real tiles.

Edge trim is taken from the room you already typed rather than asked for twice. It is the perimeter, which is where trim, edging, or a cut against the skirting runs.