How is the tile count calculated?

The area to cover is divided by the area of one tile, multiplied by one plus the waste percentage, and then rounded up to whole tiles. The multiplication happens before the rounding, so the allowance is taken on the exact count rather than an already-rounded one.

How does it work out the boxes?

It divides the tiles needed by the tiles per box and rounds up. The tiles-per-box figure comes from you: it varies by range and format, and the packaging states it — Mosa, for example, encodes the box type and piece count in the article code printed on the carton.

What is the difference between the waste allowance and the spares?

The allowance is the margin you chose, and it is already inside the tiles-needed figure. The spares are what is left after rounding up to whole boxes, and they exist only because a box cannot be split. Both are shown separately so you can see which is which.

What waste percentage should I use?

Around 10% for a straight layout in a simple room — Daltile suggests roughly that much as attic stock. Diagonal and herringbone patterns, large-format tiles and rooms with many corners or pipe penetrations need 15–20%. The right number depends on the room, which is why it is a field rather than a constant.

Does it account for grout joints?

Only through the size you enter. This is an area model: it divides the area to cover by the area of one tile and never lays out rows, so it has no geometry to place joints in. Tiles are usually sold by their laying module — Mosa states that a 15 × 15 cm modular tile is a 147 × 147 mm piece meant for a 3 mm joint — so entering the module counts the joints in, and entering the bare piece size leaves them out and slightly overstates the count. For thin joints that difference sits inside the waste allowance; for large tiles with wide joints, use the module.

Can I use it for walls?

Yes. Enter the wall area instead of the floor area; the maths is the same. Deduct doors and windows yourself, or run each wall separately.

Can I share a calculation?

Yes. Share copies a link that reopens the calculator with the same area, tile size, waste and box quantity, and download saves a plain text file with the inputs, the tile count, the boxes and the spares.

Tile calculator

Enter the area and one tile's size in metric or US customary units, add a waste percentage for cuts and breakage, and give the number of tiles in a box. The calculator shows the tiles you need, the whole boxes to buy, the tiles you end up with, and the spares that remain on top of the allowance.

Written by Kenneth Schrøder, Founder of WiseCalcs

Updated September 7, 2026·Sources verified September 7, 2026

Tiles needed is the area divided by the area of one tile, multiplied by one plus the waste percentage, rounded up. Boxes are that figure divided by the tiles per box, rounded up again — which is why you almost always end up with more tiles than you asked for.

Tiles needed (waste included)

147

Covers the floorYour waste allowanceWhole-box surplus

Whole boxes to buy: 15
Tiles you end up with: 150
Spare beyond the allowance: 3
Area to cover: 12 m²
Tiles before waste: 134
Area per tile: 0.09 m²

Two different kinds of extra: the waste allowance you chose is already inside the tiles-needed figure, and the spare on top of it exists only because boxes cannot be split.

The result updates as you type. The headline already includes your waste allowance. The bar splits the tiles you buy into the ones that cover the floor, the allowance you chose, and the extra that exists only because boxes cannot be opened halfway.

How does it work?

The waste multiplier is applied before rounding, so the allowance is taken on the exact tile count rather than on an already rounded one. The two kinds of extra are separate: the allowance is inside n, and the spare exists only because you buy whole boxes. This is an area model — it divides one area by another and does not lay out rows, so it cannot say which cuts fall where. Joints are handled by the size you enter, not by geometry: a tile sold as a 15 cm module is typically a 147 mm piece laid with a 3 mm joint, so entering the module counts the joint in and entering the piece leaves it out, which slightly overstates the count. Overstating is the safe direction.

Tiles, boxes and what is left over

n = \left\lceil \frac{A}{a}\left(1+\tfrac{w}{100}\right) \right\rceil,\quad b = \left\lceil \frac{n}{p} \right\rceil,\quad \text{spare} = b\,p - n

A: Area to cover — length × width, in metres or feet.
a: Area of one tile, from the tile size in centimetres or inches.
w: Waste allowance in percent, for cuts, breakage and spares.
n: Tiles needed, waste included. Rounded up to whole tiles.
p: Tiles per box, from the box label.
b: Whole boxes to buy.
spare: Tiles beyond n, left over because boxes cannot be split.

Metric: a 4 m × 3 m floor is 12 m². With 30 cm × 30 cm tiles each covering 0.09 m², the bare count is 133.3, so 134 tiles cover it and a 10% allowance takes that to 147. At 10 tiles a box that is 15 boxes, 150 tiles, and 3 spare on top of the allowance. US: a 12 ft × 10 ft floor is 120 ft² and 12 in × 12 in tiles cover 1 ft² each, so 120 tiles bare, 132 with 10% waste, 14 boxes of 10, 140 tiles, 8 spare.

Method & sources

Metric mode takes metres for the area and centimetres for the tile; US customary mode takes feet and inches. Switching converts the numbers, so the room and the tile stay the same size. Tiles are counted by area — the area to cover divided by the area of one tile. No layout is generated and no cuts are predicted. The waste percentage covers cuts, breakage and spares, and is yours to set. Daltile suggests about 10% as attic stock.

Sources

Where this method comes from — use these references to understand the formula, assumptions, and limits.

Mosa Glazed Wall Tiles — technical product sheet W14-01 US (modular vs manufacturing size, packaging code) — Koninklijke Mosa bv, verified 2026-09-07
Daltile tile and stone FAQs — ordering about 10% extra as attic stock from the same dye lot — Daltile (Dal-Tile LLC), verified 2026-09-07

How we calculate

Metric mode takes metres for the area and centimetres for the tile; US customary mode takes feet and inches. Switching converts the numbers, so the room and the tile stay the same size.
Tiles are counted by area — the area to cover divided by the area of one tile. No layout is generated and no cuts are predicted.
The waste percentage covers cuts, breakage and spares, and is yours to set. Daltile suggests about 10% as attic stock.
Tiles per box comes off the box label; the default is only a starting value.
Counts round up to whole tiles, and boxes round up to whole boxes.
Joints are handled by the size you type, not by geometry: enter the laying module to include the joint, or the piece size to leave it out.

Limitations

It divides one area by another. It cannot say where the cuts fall, how a pattern lands at the edges, or how many tiles a particular layout wastes — that is what the waste percentage stands in for.
Setting out a diagonal or herringbone pattern wastes noticeably more than a straight grid, but the calculator has no view on which pattern you use beyond the percentage you enter.
Box quantities differ between ranges and formats, so the tiles-per-box default is a placeholder for the number on your own packaging.

Rounding

Tile and box counts round up to whole units; areas are shown to a few decimals. The waste multiplier is applied to the exact tile count before it is rounded up, so the allowance is never taken on an already-rounded number.

What this calculator does

Tiles are planned by area but sold by the box, so this calculator does both halves. It divides the area to cover by the area of one tile, adds the waste percentage you set, and rounds up to whole tiles. Then it divides that by the number of tiles in a box, rounds up again, and tells you how many tiles you will actually own and how many are spare.

It works in metres and centimetres or in feet and inches, and switching converts the numbers rather than reinterpreting them — a 30 cm tile becomes an 11.81 in tile, not a 30 in one, so the count does not move when the units do.

How to measure and use it

Pick metric or US customary units.
Enter the length and width of the area to cover.
Enter one tile's length and width — centimetres in metric, inches in US.
Set the waste percentage. 10% suits a straight layout in a simple room; diagonal and herringbone patterns and rooms full of corners need more.
Copy the tiles per box off the box label.
Buy the whole-box figure, and check the spares before you decide the box size is right.

A worked example

A 4 m × 3 m floor is 12 m². With 30 cm × 30 cm tiles, each covering 0.09 m², the bare count is 133.3, so 134 tiles cover the floor and a 10% allowance takes it to 147. At 10 tiles a box that is 15 boxes, 150 tiles, and 3 spare beyond the allowance.

In US units: a 12 ft × 10 ft floor is 120 sq ft, and 12 in × 12 in tiles cover 1 sq ft each, so 120 tiles bare, 132 with 10% waste, 14 boxes of 10, 140 tiles, and 8 spare.

Two different kinds of extra

The waste allowance and the box surplus are not the same thing, and confusing them leads to buying twice over. The allowance is a margin you choose for cuts, breakage and future repairs, and it is already inside the tiles-needed figure. The surplus on top of that is arithmetic: boxes cannot be split, so the last box comes home whether you need all of it or not.

It is worth looking at both before you order. If the spares are already generous, a smaller waste percentage may cost you nothing. If they are almost nil, one extra box is cheap insurance — matching a dye lot later is difficult, which is exactly why Daltile recommends keeping about 10% as attic stock rather than buying to the metre.

Choosing a waste percentage

Straight layouts in a simple rectangular room need about 10%. Diagonal or herringbone patterns cut every tile at the edges and often need 15–20%, and so do rooms with alcoves, recesses and pipe penetrations. Large-format tiles waste more because each mistake costs more area. This is guidance for choosing the number, not a claim about your layout: the calculator has no idea what pattern you are laying and cannot optimise one for you.

Tile size, joints and the module

A tile is usually slightly smaller than the size it is sold as, because the nominal size is the module it is laid at — the tile plus its joint. Mosa's technical sheet for its glazed wall tiles states it plainly: a modular size of 15 × 15 cm is a manufacturing size of 147 × 147 mm, intended for a 3 mm joint. Over a wall it is the 15 cm module that repeats, not the 147 mm piece.

So the joint is handled by which number you type, not by any geometry inside the calculator. Enter the module and the joints are already counted; enter the bare piece and they are not, which overstates the tile count slightly. Overstating is the safe direction, and for small joints the difference is well inside the waste allowance — but for a large-format tile with a wide joint it is worth using the module.

Common mistakes

Entering the tile size in the wrong unit — metres instead of centimetres, or feet instead of inches.
Treating the spares from box rounding as if they were the waste allowance, and then cutting the allowance to match.
Buying to the exact tile count with no allowance at all.
Ordering a second batch later. Shade varies between production runs, so buy the whole job at once.
Assuming the box quantity from a previous job. It changes with the range and the format.

When it's useful

Planning a floor, splashback, bathroom or patio — any tiling job where you need to turn an area into an order in boxes before you start.

FAQ

How is the tile count calculated?: The area to cover is divided by the area of one tile, multiplied by one plus the waste percentage, and then rounded up to whole tiles. The multiplication happens before the rounding, so the allowance is taken on the exact count rather than an already-rounded one.
How does it work out the boxes?: It divides the tiles needed by the tiles per box and rounds up. The tiles-per-box figure comes from you: it varies by range and format, and the packaging states it — Mosa, for example, encodes the box type and piece count in the article code printed on the carton.
What is the difference between the waste allowance and the spares?: The allowance is the margin you chose, and it is already inside the tiles-needed figure. The spares are what is left after rounding up to whole boxes, and they exist only because a box cannot be split. Both are shown separately so you can see which is which.
What waste percentage should I use?: Around 10% for a straight layout in a simple room — Daltile suggests roughly that much as attic stock. Diagonal and herringbone patterns, large-format tiles and rooms with many corners or pipe penetrations need 15–20%. The right number depends on the room, which is why it is a field rather than a constant.
Does it account for grout joints?: Only through the size you enter. This is an area model: it divides the area to cover by the area of one tile and never lays out rows, so it has no geometry to place joints in. Tiles are usually sold by their laying module — Mosa states that a 15 × 15 cm modular tile is a 147 × 147 mm piece meant for a 3 mm joint — so entering the module counts the joints in, and entering the bare piece size leaves them out and slightly overstates the count. For thin joints that difference sits inside the waste allowance; for large tiles with wide joints, use the module.
Can I use it for walls?: Yes. Enter the wall area instead of the floor area; the maths is the same. Deduct doors and windows yourself, or run each wall separately.
Can I share a calculation?: Yes. Share copies a link that reopens the calculator with the same area, tile size, waste and box quantity, and download saves a plain text file with the inputs, the tile count, the boxes and the spares.

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