Why use this calculator
Running short of tiles is worse than it sounds. Tiles are made in batches, and the next batch can differ in shade and even in size by enough to show on the floor, so the box you buy to finish a job may never match.
The fix is to buy the right quantity once, from one batch, with a sensible allowance for cuts and breakage. This calculator does that properly. It includes the grout joint, which changes how many tiles cover each square metre, applies a wastage allowance you choose for the laying pattern, rounds up to whole boxes using the count printed on the box, and gives the adhesive and grout you will need so one trip to the supplier covers everything.
A table shows how the order changes for straight, offset, diagonal and herringbone patterns so you can price each option before choosing.
How to use it
- Choose metric or imperial units.
- Enter the area length, measuring the longest side of the floor or wall.
- Enter the width, or the height to be tiled for a wall.
- Enter the tile length and width from the box, using the actual face size.
- Enter the grout joint width you intend to use, typically 2 to 3 mm for rectified porcelain.
- Enter the tile thickness, which drives the grout quantity.
- Enter the tiles per box from the box label.
- Finally set the wastage allowance, 10 per cent for a straight lay and more for diagonal or herringbone patterns.
What each result means
- Tiles to order
- The number of tiles to buy including your wastage allowance for cuts, breakage and pattern matching at the edges.
- Boxes to buy
- Tiles to order rounded up to whole boxes. Buy them all at once from the same batch or shade code.
- Tiles before wastage
- Tiles that would exactly cover the area with no cuts or breakage. Useful for checking a quote that looks light.
- Area to tile
- Length multiplied by width in square metres or square feet, the figure suppliers price and quote against.
- Area covered by the boxes
- The laid coverage of every tile in the boxes you buy, including joints. It should comfortably exceed the area to tile.
- Tile adhesive
- Cement-based adhesive at a typical rate for this tile size, rounded up to whole bags. Large tiles need a bigger notch trowel and more adhesive.
- Grout
- Grout to fill the joints to full tile depth, with a small allowance for mixing and cleaning losses.
The formula
Laid area per tile
(m²) = (L + j) x (W + j) / 1,000,000
Tiles before wastage = area to tile (m²) / laid area per tile
Tiles to order = round up (tiles before wastage x (1 + wastage % / 100))
Boxes = round up (tiles / tiles per box)
Grout (kg) = area x (L + W) / (L x W) x j x t x 1.6 x 1.1
- t
- tile thickness in mm
- 1.6
- grout density in kg per litre and 1.1 allows 10 per cent loss
Adhesive uses 3, 4 or 6 kg per m² for small, medium and large format tiles.
How this number is used in practice
Wastage allowances are trade rules of thumb and they matter. A straight lay in a simple rectangular room wastes about 10 per cent, because one row on each side is cut and a few tiles break. A brick or one-third offset lay adds a little.
A diagonal lay cuts every edge tile at 45 degrees and needs about 15 per cent, and herringbone or chevron needs 20 per cent or more. Large format tiles in a small room waste more still, because each cut discards a big piece. Keep at least a few spare tiles after the job for future repairs, since the batch will be gone.
Adhesive quantity depends on the trowel. Australian and UK manufacturers quote roughly 2.5 to 3 kg per m² with a 6 mm notch for small wall tiles, about 4 kg per m² with a 10 mm notch for standard floor tiles, and 5 to 7 kg per m² with a 12 mm notch plus back buttering for tiles 600 mm and larger.
AS 3958.1 in Australia, the TCNA Handbook in the US and BS 5385 in the UK all require near full coverage for floors and wet areas, which large tiles only reach with back buttering.
In wet areas the tile is not the waterproofing. The membrane beneath it is, and in Australia it must meet AS 3740 and be installed by a licensed or certified waterproofer in most states.
Worked examples
A 3.6 x 3.0 m bathroom floor, 600 x 300 mm porcelain, 3 mm joints, 8 per box, 10% wastage
66 tiles, 9 boxes, 65 kg of adhesive (4 x 20 kg bags) and 2.9 kg of grout
A 12 x 10 ft kitchen in 12 x 24 inch tiles, 1/8 inch joints, 8 per box, laid on the diagonal at 15%
68 tiles, 9 boxes covering 146.26 sq ft
A 2.4 x 2.2 m shower wall in 100 x 100 mm mosaic-style tiles, 2 mm joints, 100 per box, 15% wastage
584 tiles, 6 boxes and about 16 kg of adhesive
When people use it
- Ordering floor tiles for a bathroom, kitchen or laundry in one trip
- Pricing a diagonal or herringbone lay against a straight lay before committing
- Checking a tiler's quoted quantities for a renovation
- Estimating adhesive and grout bags alongside the tiles
- Working out wall tiles for a shower recess or splashback
Tips
- Buy every box from the same batch and check the shade code on each label before opening.
- Keep five to ten spare tiles after the job for future repairs. Matching them later is rarely possible.
- Measure after walls are sheeted and before cabinets go in if the floor tiles run under them.
- Dry lay a row in each direction to plan cuts so edge tiles are not slivers under half a tile.
- Use a levelling clip system for tiles 600 mm and larger to control lippage.
- Mix only as much adhesive as you can use within its open time, usually 20 to 30 minutes.
What it assumes, and where it stops being accurate
- The area is a rectangle. Measure irregular rooms as several rectangles and add the results.
- Wastage is a single percentage. Complex rooms with columns, curves or many penetrations may need more.
- Adhesive rates are typical cement-based figures by tile size. The product's own coverage chart is the authority.
- Grout is calculated for full-depth joints at a density of 1.6 kg per litre. Epoxy and sanded grouts differ.
- Box counts vary by manufacturer. Always use the figure on the box you are buying.
- Skirting, trims, membranes and levelling compound are not included.
Terms used on this page
- Rectified tile
- A tile ground to precise dimensions after firing, allowing very narrow grout joints.
- Batch or shade code
- The production run printed on the box. Tiles from one code match in colour and size.
- Notch trowel
- A trowel with square or U notches that sets the adhesive bed thickness.
- Back buttering
- Spreading a thin layer of adhesive on the back of a tile to achieve full coverage.
- Lippage
- A height difference between the edges of adjoining tiles.
Questions people ask
- How much extra tile should I buy?
- Allow 10 per cent for a straight lay in a simple room, 12 per cent for a brick or offset lay, 15 per cent for a diagonal lay and 20 per cent for herringbone. Add more for small rooms with large tiles or many obstacles, and keep a few spares for repairs.
- Why does the grout joint change the number of tiles?
- Each tile covers its own face plus half a joint on every side. With 600 by 300 mm tiles and 3 mm joints, each tile lays about 0.183 m² rather than 0.180 m², so you need slightly fewer tiles. With small mosaics the joint makes a larger difference.
- How much tile adhesive do I need?
- Roughly 3 kg per m² for small wall tiles, 4 kg per m² for standard floor tiles with a 10 mm notch trowel, and 6 kg per m² for large format tiles that are back buttered. Always check the coverage chart on the bag you are using.
- Should I tile under kitchen cabinets?
- It is common to stop at the cabinet line to save tiles, but tiling underneath lets you change the kitchen later without patching the floor. Either way, measure the area you will actually tile and enter that rather than the whole room.
- Why must all the tiles come from one batch?
- Kiln conditions vary between production runs, so shade, and sometimes the exact calibre or size, differ from batch to batch. Mixing batches can show as a visible patch or uneven joints, which is why suppliers print a batch and shade code on each box.
Use this with
Tile Calculator answers one part of the question. These pick up where it stops: Flooring Calculator, Paint Calculator, Area Calculator and Brick and Block Calculator.
Where these figures come from
This calculation is jurisdiction-neutral arithmetic. No country-specific rules are applied.
- Tile Council of North America. TCNA Handbook installation methods and coverage requirements
- Standards Australia. AS 3958.1 ceramic tile installation and AS 3740 wet area waterproofing
- The Tile Association (UK). UK guidance aligned with BS 5385
Tile Calculator produces an estimate for general information. It is not financial, tax, medical, legal or engineering advice. read the full disclaimer. Spotted a wrong number? Report it and it gets fixed. The form picks up this calculator and the inputs you used.