How many tiles do I need? Three rooms worked through, piece by piece

Short answer: work the surface out in square metres, take off the openings and anything you are not tiling, divide by the face area of one tile, add an allowance for cuts and breakage, then round up to whole pieces and, for a tile sold by the box, to whole boxes. A 600 × 1200 mm tile has a face of 0.72 m², a 300 × 600 mm tile 0.18 m², a 75 × 300 mm subway tile 0.0225 m², and a 306 × 306 mm mosaic sheet 0.0936 m². Order the whole job in one go rather than topping up later. The tile calculator runs that sum for you, allowance and rounding included — this guide does it by hand on three surfaces so you can see where every figure comes from.

What sum is the calculator actually doing?

One line, and it does not change from room to room:

(surface area − deductions) × (1 + allowance) ÷ face area of one tile = pieces, rounded up

The tile calculator takes each surface in metres, subtracts the openings you enter, applies the allowance you choose, and turns the result into whole pieces from the tile dimensions in millimetres. Its allowance buttons read 10 %, 15 % and 20 %, and the page says those are example inputs rather than recommendations. What tile brands, retailers and a tiler publish by laying pattern, tile size and room is set out, with sources, in tile wastage percentage by pattern, size and room.

Three surfaces follow: a bathroom floor in a large format, the walls of the same bathroom to 2,100 mm, and a kitchen splashback counted twice, in subway pieces and in mosaic sheets. The room dimensions are assumptions, chosen so the arithmetic is visible; substitute your own. The tile sizes are not: each is the size row on a product page, quoted at the end. Which dimension a page states is set out in tile sizes in Australia, and the tiles per square metre and per box for every size here are set out in one table.

How many tiles do I need for a bathroom floor?

Assume a floor 3.0 × 2.1 m with a moulded shower base 0.9 × 0.9 m standing on it, so that square is not tiled. The tile is Pietra Vela Marble-Look Tile, one of the 600 × 1200 mm tiles; its page states Size: 600 × 1200 mm, a face of 0.72 m², or 1.39 tiles to the square metre. Running this arithmetic on a floor is not a statement that this tile, or any tile here, belongs on a floor: where a tile can go is a question for your tiler and the supplier's documentation, not for this guide.

Nine pieces. Where the courses land is a separate question from how many to order. Run the 1,200 mm edge down the 3.0 m length and two whole tiles reach 2,402 mm with a 2 mm joint, leaving a 596 mm cut, near enough half a tile. Across the 2.1 m width the 600 mm edge gives three whole tiles to 1,804 mm and a 294 mm strip. So the floor is a grid three wide and four deep: twelve positions, most cut on at least one edge.

Twelve positions against nine pieces ordered is not a contradiction. Twelve uncut tiles would be 8.64 m² of tile on a 5.49 m² floor; the offcut from one position becomes the cut at the next, which is why the count is done on area rather than by counting positions on a sketch. Where it strains is a long, narrow cut whose offcut fits nowhere else; the tiler setting the job out is the one who can say.

In boxes: the Pietra Vela page gives Box coverage: 2 pieces, 1.44 m², 30 kg per box, so 9 pieces is 5 boxes at either allowance, 10 pieces in all, 1 more than the count. Rounding to whole boxes adds that piece on top of the allowance; it is not a reason to lower the allowance.

How many tiles for the bathroom walls at 2,100 mm?

Same room, so 2 × (3.0 + 2.1) = 10.2 m of wall. Take the tiling to 2,100 mm. There is an arithmetic argument for that height as well as a visual one: the top edge lands level with a standard door head, so the whole door opening — here 0.80 × 2.00 m, 7.5 % of the gross wall — comes off in one clean rectangle, and the edge has a line already on the wall to sit beside. Half wall or floor to ceiling weighs 2,100 mm against a half wall and full height; this guide takes the height as settled and counts.

The tile is Pietra Neve Marble-Look Tile, from the 300 × 600 mm tiles; its page states Sizes: 300 × 600 mm; 600 × 600 mm, and since 5 October 2026 you choose one of the two with a button on the page. Take the 300 × 600: a face of 0.18 m², 5.56 tiles to the square metre. Assume one window, 1.0 × 0.6 m, wholly inside the tiled band.

Which way the tile goes on does not change the count — 0.18 m² is 0.18 m² lying down or standing up — but it moves every joint. Laid flat, courses are 300 mm: six reach 1,810 mm and the seventh is cut to 288 mm. Stood upright, courses are 600 mm: three reach 1,804 mm and the top piece is 294 mm. Sideways along the 3.0 m wall, four whole 600 mm widths reach 2,406 mm and leave a 592 mm cut in one corner, or two matching 295 mm cuts set out from the centre. The 2.1 m wall takes three widths to 1,804 mm and a 294 mm cut, or two of 146 mm.

One decision is worth putting a figure on. The wall behind a 0.9 × 0.9 m vanity is 0.81 m². Skipping it saves 4.2 % of the net wall area and five pieces — small against the day a replacement vanity of a different width leaves bare wall showing.

In boxes: with 300 × 600 mm selected, the page's Box coverage row gives 8 pieces, 1.44 m² per box. That is the typical pack for this size: the page says the supplier's current documentation does not state it, so confirm it before ordering. On that pack 118 pieces is 15 boxes (120 pieces) and 123 is 16 (128). Select 600 × 600 mm instead and the box is the supplier's own, 4 pieces, 1.44 m², 30 kg; the same wall at 10 % is then 21.142 ÷ 0.36 = 58.73, 59 pieces, and still 15 boxes, because both boxes cover 1.44 m².

How many tiles for a kitchen splashback?

Assume a bench run 3.6 m long with 0.6 m between the bench and the overhead cupboards, plus a 0.9 m panel behind the cooktop carried 0.15 m higher. One window over the sink, 1.0 × 0.6 m, comes off the full height of the strip.

Count it twice. First in Studio Greige Subway Tile, one of the subway tiles, whose page states Size: 75 × 300 mm — 0.0225 m² a piece, 44.44 pieces to the square metre. Then in Carrara Square Mosaic Tile, one of the mosaic tiles and the only sheet in square mosaic tiles, whose page states Sheet size: 306 × 306 mm — 0.093636 m² a sheet, 10.68 sheets to the square metre. A mosaic is counted in sheets, never in chips: the sheet is the unit the page states and the unit the sum divides by. How to measure a tiling project goes further into sheets and why sheet sizes differ between designs; this guide does not repeat it.

A 600 mm strip looks made for a 75 mm subway course: eight courses, 600 mm, exactly. Add a 2 mm joint and those eight stand 614 mm, fourteen millimetres too tall, so seven whole courses reach 537 mm and the eighth is cut to 61 mm. A 61 mm sliver under a cupboard is the sort of thing a tiler will move by adjusting the joint width or lifting the first course. Along the run, eleven whole tiles reach 3,320 mm and leave 278 mm, or 138 mm at each end if set out from the centre.

The sheets land the same way: two rows of 306 mm also come to 614 mm, so one whole row goes on and the second is cut to 292 mm. Along the 3.6 m run eleven sheets reach 3,386 mm and leave 212 mm, or two cuts of 105 mm. Kitchen splashback tiles: nine formats compared sets the two side by side, and kitchen splashback tiles is the full list. To take the same wall higher, to the rangehood or the ceiling, and turn each height into boxes, see Kitchen wall tiles: how high to tile and how many boxes.

In boxes, the subway count is two: the Studio Greige page gives Box coverage: 44 pieces, 1 m², 16 kg per box, so 83 pieces at 10 % is 1.89 boxes and 87 at 15 % is 1.98, two boxes either way, 88 pieces. The mosaic has no box to convert to: Carrara Square is sold by the sheet, so the sheet count is the order.

A laundry splashback is counted the same way: laundry tile ideas works a 1.8 m bench through in boxes and in mosaic sheets.

How much should I add for cuts, 10 % or 15 %?

Ten per cent is the figure most people work to on a straight-laid job in a square room. Fifteen is the common one for a diagonal or herringbone layout, where every piece at the perimeter is cut and the offcuts come off as triangles that fit nothing else. Both are working figures — ordinary practice, not a rule this site sets or verifies — and the tiler doing the job sets the real one. An awkward room, a pattern that lines up across a corner, or a run of long thin cuts all argue upwards.

What the step from 10 % to 15 % adds in pieces is less than it sounds, and it shrinks as the tile grows. On the bathroom wall it is five pieces, 118 against 123. On the splashback it is four, 83 against 87. On the floor it is nothing at all — 9 either way — because one 600 × 1200 mm tile is 13.1 % of that whole floor, so the rounding absorbs the difference. The larger the format, the coarser the rounding. In boxes the step is one box on the wall, 15 against 16, and none on the floor or the splashback.

Should I order the whole job at once?

Yes, and this is the one part that is not arithmetic. Every product page here carries the same line: production batches can vary. A top-up ordered weeks later can come from a different run and sit visibly beside the first, so apply the allowance once, to the whole job, not surface by surface. The three surfaces above come to 26.4 m² net: 9 floor pieces and 118 wall pieces, 127 in all, plus 20 mosaic sheets. In boxes that is 5 of Pietra Vela and 15 of Pietra Neve, plus the 20 sheets. If you have not seen a face in person, order a sample before committing to a quantity, and what to check when buying tiles online covers the rest.

Where these facts come from

The four tile sizes were read from the Specifications panel of the product pages linked above on 15 September 2026: Pietra Vela Marble-Look Tile, Size: 600 × 1200 mm; Pietra Neve Marble-Look Tile, Sizes: 300 × 600 mm; 600 × 600 mm; Studio Greige Subway Tile, Size: 75 × 300 mm; Carrara Square Mosaic Tile, Sheet size: 306 × 306 mm. The method and the 10 %, 15 % and 20 % allowance options come from the tile calculator page. Room dimensions, the 2 mm joint and the two allowances are assumptions, stated where they are used. Box coverage was read from the same pages on 5 October 2026: Pietra Vela, 2 pieces, 1.44 m², 30 kg per box, and Studio Greige, 44 pieces, 1 m², 16 kg per box, both from supplier documentation since 2 October 2026; for Pietra Neve at 300 × 600 mm the page uses the typical pack of 8 pieces, 1.44 m² per box, which the supplier's current documentation does not state. Quantities are in pieces, boxes, sheets and square metres only. Nothing here is a performance claim or a statement about where a particular tile belongs; confirm the final quantity, the joint width and the set-out with the tiler doing the work.

Where this guide sits: Where to start sets out the order the guides follow.

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