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How to use this calculator#
- Measure the area, subtracting only fixed obstructionsTake length × width for a floor, or height × width for a wall. Subtract a shower tray, a bath or a built-in unit that will never move. Do not subtract a freestanding cooker or a washing machine — tile under those so they can be pulled out.
- Work out the area of a single tileMultiply the two tile dimensions in metres, or in inches then divide by 144 for square feet. A 300 × 600 mm tile is 0.3 × 0.6 = 0.18 m². A 12 × 24 in tile is 288 ÷ 144 = 2 sq ft.
- Divide, then add the waste allowance for your layoutStraight grid in a square room: 10%. Brick or offset bond: 10–12%. Diagonal at 45 degrees: 15%. Herringbone, chevron or hexagon: 15–20%. Small rooms with many fixtures and large-format tiles both push toward the top of the range.
- Round up to whole boxesMerchants rarely split a box. Divide your tile count by the tiles per box and round up, then buy one spare box on top for future repairs — matching a discontinued line in three years' time is close to impossible.
- Check every box carries the same batch numberTiles are fired in batches and shade varies visibly between them. Inspect the batch or shade code on each box at the merchant, and mix tiles from several boxes as you lay so any variation is spread rather than banded.
The formula#
Tile count from area
tiles = (area ÷ tile area) × (1 + waste) • boxes = ⌈tiles ÷ tiles per box⌉
- area
- The surface being tiled, in m² or sq ft, after deducting fixed obstructions
- tile area
- Length × width of one tile in the same unit — 0.3 × 0.6 = 0.18 m² for a 300 × 600 mm tile
- waste
- 0.10 for a straight layout, 0.15 for diagonal, up to 0.20 for herringbone or a small cut-heavy room
- ⌈ ⌉
- Round up — boxes are sold whole
The calculation uses the nominal tile size and ignores grout joints, which makes the count very slightly conservative: a 300 mm tile with a 3 mm joint really occupies 303 mm, so a large floor holds about 2% fewer tiles than the arithmetic suggests. Your waste allowance absorbs that. The trap is unit consistency — a tile size in millimetres against an area in square feet produces a meaningless number, so convert one to match the other before dividing.
Tiles, boxes and the waste allowance#
Divide the area being tiled by the area of a single tile, then add waste. A 300 by 600 mm tile covers 0.18 square metres, so a 12 square metre floor needs 67 tiles before any allowance. Ten percent is standard for a straight, square room; go to 15% for diagonal or herringbone layouts and 20% for small rooms with lots of cuts or a hexagon format.
Buy by the box, and buy the same batch#
Tiles ship in boxes — commonly 6 to 12 for large formats and far more for mosaics — and merchants rarely split them, so round up to whole boxes. Every box carries a batch or shade number, and tiles from different batches can differ visibly in tone. Order the whole job at once and keep a spare box, because matching a discontinued line three years later is close to impossible.
Grout joints and setting out#
Joint width shifts the count more than people expect. A 300 mm tile with a 3 mm joint effectively occupies 303 mm, adding about 2% across a large floor; this calculator ignores joints, so your waste allowance absorbs that. Set out from the centre of the room so cuts fall evenly at both walls, and never plan a cut narrower than a third of a tile where it will be seen.
Worked examples#
A bathroom floor in 300 × 600 mm tiles
A floor 2.4 m by 1.8 m, straight-laid, with a 0.9 × 0.9 m shower tray in one corner. Tiles come 8 to a box.
- Gross area = 2.4 × 1.8 = 4.32 m²
- Deduct the tray: 0.9 × 0.9 = 0.81 m², leaving 3.51 m²
- Tile area = 0.3 × 0.6 = 0.18 m²
- Tiles before waste = 3.51 ÷ 0.18 = 19.5, so 20
- Small room with many cuts, so use 15%: 19.5 × 1.15 = 22.4, round to 23 tiles
- Boxes = 23 ÷ 8 = 2.9, so 3 boxes (24 tiles)
3 boxes. That leaves one spare tile, so buy a fourth box if you want a genuine repair stock.
A living-room floor in 12 × 24 in tiles
A 15 × 20 ft room laid in a brick bond offset, tiles 6 to a box at $42 a box.
- Area = 15 × 20 = 300 sq ft
- Tile area = (12 × 24) ÷ 144 = 2 sq ft
- Tiles before waste = 300 ÷ 2 = 150
- Offset bond in a square room, use 12%: 150 × 1.12 = 168 tiles
- Boxes = 168 ÷ 6 = 28 boxes exactly
- Cost = 28 × $42 = $1,176
28 boxes, $1,176 in tile. Add adhesive, grout, spacers and trim, which typically run 15–25% on top of the tile cost.
Reference tables#
| Tile size | Area of one tile | Tiles per m² | Tiles for 10 m² | With 10% waste |
|---|---|---|---|---|
| 100 × 100 mm | 0.0100 m² | 100.0 | 1,000 | 1,100 |
| 150 × 150 mm | 0.0225 m² | 44.4 | 445 | 489 |
| 200 × 200 mm | 0.0400 m² | 25.0 | 250 | 275 |
| 250 × 400 mm | 0.1000 m² | 10.0 | 100 | 110 |
| 300 × 300 mm | 0.0900 m² | 11.1 | 112 | 123 |
| 300 × 600 mm | 0.1800 m² | 5.6 | 56 | 62 |
| 400 × 400 mm | 0.1600 m² | 6.3 | 63 | 69 |
| 450 × 450 mm | 0.2025 m² | 4.9 | 50 | 55 |
| 600 × 600 mm | 0.3600 m² | 2.8 | 28 | 31 |
| 600 × 1200 mm | 0.7200 m² | 1.4 | 14 | 16 |
Halving a tile's dimensions quarters its area, so the count goes up fourfold. A 150 mm mosaic-scale tile takes sixteen times as many pieces per square metre as a 600 mm format.
| Tile size | Area of one tile | Tiles per 100 sq ft | With 10% waste |
|---|---|---|---|
| 4 × 4 in | 0.111 sq ft | 900 | 990 |
| 6 × 6 in | 0.250 sq ft | 400 | 440 |
| 8 × 8 in | 0.444 sq ft | 225 | 248 |
| 12 × 12 in | 1.000 sq ft | 100 | 110 |
| 16 × 16 in | 1.778 sq ft | 57 | 62 |
| 12 × 24 in | 2.000 sq ft | 50 | 55 |
| 18 × 18 in | 2.250 sq ft | 45 | 49 |
| 24 × 24 in | 4.000 sq ft | 25 | 28 |
One square metre is 10.764 sq ft, so a figure quoted per 100 sq ft covers 9.29 m².
| Layout or situation | Waste allowance | Why |
|---|---|---|
| Straight grid, square room | 10% | Cuts only at the perimeter, all on two axes |
| Brick or offset bond | 10–12% | Every other row starts with a half tile |
| Diagonal (45 degrees) | 15% | Every perimeter tile is cut, and the offcuts are triangles |
| Herringbone or chevron | 15–20% | Angled cuts at both ends and heavy offcut loss |
| Hexagon and other shaped formats | 15–20% | Perimeter cuts rarely yield a usable second piece |
| Small or irregular room, many fixtures | 15–20% | High ratio of cut tiles to whole tiles |
| Large format over 600 mm | 15% | Fewer, more expensive pieces and a higher breakage risk |
| Natural stone with shade variation | 15–20% | Some pieces are rejected on appearance, not on fit |
Whatever the allowance, buy one extra box beyond it and store it. A repair tile from the same batch is worth far more than the box costs.
Common mistakes#
- Forgetting the waste allowance entirelyOrder exactly 150 tiles for a floor that measures 150 tiles and you will finish two rows short, because every perimeter tile is cut and most offcuts are unusable. On a diagonal layout the shortfall is closer to 15%, which is more than twenty tiles.
- Mixing metric tile sizes with an imperial areaDividing 300 sq ft by 0.18 m² produces 1,667 — a number with no meaning at all. Convert first: 300 sq ft is 27.87 m², which at 0.18 m² per tile is 155 tiles. The unit mismatch inflates the count more than tenfold.
- Buying boxes from different batchesEvery box carries a batch or shade code, and tiles fired at different times differ visibly in tone. Topping up later almost always means a different batch, and the join reads as a stripe across the floor under raking light.
- Ignoring the setting-out before orderingStarting from a wall rather than the centre of the room pushes all the cuts to one side, and a sliver narrower than about a third of a tile looks like a mistake and is fragile. Setting out from the centre balances the cuts and often changes the tile count.
Frequently asked questions#
How much extra tile should I buy for waste?
Ten percent for a simple straight layout, 15% for diagonal or herringbone patterns, and up to 20% for small or irregular rooms with many cuts.
How many tiles are in a box?
It varies with size — typically 6 to 12 for 300 by 600 mm formats and 4 to 6 for large-format tiles. The box label always states coverage in square metres or square feet.
How do I calculate tiles for a wall?
Use wall height times width for the area and subtract windows or a shower niche. Wall tiling usually needs a slightly higher waste allowance because of cuts around fittings.
Should I tile under kitchen units?
Tiling under freestanding appliances is wise so they can be pulled out later. Under fixed units it is normally skipped, but always run tiles a few inches past the toe kick.
Key terms#
- Nominal versus actual size
- The size printed on the box is nominal. Actual pressed tiles vary by a millimetre or two, and rectified tiles are ground to precise edges so they can be laid with very narrow joints. Calculations use the nominal figure.
- Batch or shade number
- A code printed on every box identifying the production run. Tiles from different batches can differ visibly in colour and size, so all tile for one job should share a batch.
- Setting out
- Planning where the first tile goes so cuts fall evenly. Standard practice is to find the centre of the room, dry-lay a row each way, and shift the start point so no perimeter cut is narrower than about a third of a tile.
- Grout joint
- The gap between tiles, typically 2–3 mm for rectified porcelain and 3–5 mm for pressed ceramic. Joints absorb dimensional variation and allow movement; a 3 mm joint adds about 1% to the space a 300 mm tile occupies.
- Large-format tile
- Generally anything with a side over 400 mm (about 15 in). Needs a flatter substrate, a larger-notch trowel and back-buttering, and carries a higher breakage rate — which is why its waste allowance runs higher.
- Coverage per box
- The area one box tiles, printed on the label in m² or sq ft. Dividing your area by box coverage is a faster route to a box count than working through individual tiles.
Sources#
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