Tile Calculator UK · metric

Square metres of tile, adhesive, grout and cost for walls and floors. Metric units and £ costs, updated for 2026.

Last reviewed July 2026 · Free · Nothing you enter is stored

How this calculator works

Tile to buy = area plus a waste allowance for cuts and breakages. Estimates add tile adhesive (a 20 kg bag covers about 5 m²) and grout (about 8 m² per bag). Installed cost uses a UK average per m² including labour, adhesive and grout.

The waste allowance

The allowances this calculator offers, about 10% for a straight lay, 15% for a diagonal and up to 20% for herringbone and other patterns, are trade convention rather than anything published in BS 5385. They hold up well in practice and they are worth applying, but treat them as experienced guidance rather than a specification. The logic is simple enough: every cut against a wall or an obstruction leaves an offcut, and the more angles a pattern contains the less of each cut tile ends up back on the floor. There is a second, quieter source of waste in the UK, which is the box. Tile is sold by the square metre but supplied in boxes covering a fixed area, so a 10 m² floor with a 10% allowance does not buy 11 m² of tile, it buys however many whole boxes clear 11 m². Round up to boxes at the end, not before.

Buying by the square metre, and the batch number

British tile is priced and ordered in square metres, which spares you the business of counting tiles per square foot. The count still matters for setting out, and that arithmetic needs the joint included: a tile occupies its own dimension plus the joint, so 600 mm tiles at a 3 mm joint sit on a 603 mm module. Across a long room that accumulates to roughly a tile's worth, in your favour, and on small tile with wide joints it is a real fraction of the module.

Nominal sizes drift as well. Plenty of tile sold as 300 x 300 measures slightly under, by design, with the joint taking up the difference. If you are setting out closely, measure a tile out of the box rather than trusting the label, and do it before the adhesive is mixed rather than halfway along the first row.

The thing genuinely worth care is the batch. Tile is fired in production runs and shade varies between them, which is why boxes carry a batch or shade code. Two boxes of the same product from different batches can differ enough to show under raking light across a finished floor. Order the whole quantity in one go, check the codes match on delivery, and keep the spare box. A cracked tile five years from now needs a match, and the original batch will be long gone.

Adhesive: notch size, bed depth and kilograms

UK adhesive is sold in 20 kg bags and consumed according to how deep a bed you leave under the tile, which is set by the trowel. Weber's guidance pairs the notch to the tile: a 6 mm notch for tiles under 100 mm, 8 mm for 100 to 200 mm, 10 to 12 mm for tiles over 200 mm, and 15 to 20 mm for very large formats. As a rule of thumb a square notch leaves a bed about half its depth once the tile is pressed down, so a 12 mm notch gives roughly a 6 mm bed and a 6 mm notch roughly 3 mm.

Mapei publish consumption for Keraflex Maxi S1 as 1.2 kg per square metre per millimetre of bed thickness, which turns the trowel into kilograms directly. A 3 mm bed is about 3.6 kg/m², so a 20 kg bag covers around 5.5 m². A 5 mm bed is 6 kg/m² and a bag covers about 3.3 m². A 6 mm bed is 7.2 kg/m² and a bag covers under 3 m². Moving up one trowel size can nearly halve the area a bag reaches, which is the single most common reason people run short.

Two things push consumption above that arithmetic. The first is an uneven background, because adhesive is not a levelling compound and every hollow you fill comes out of the bag. The second is back-buttering, which Mapei recommend for tiles larger than 300 x 300 mm, for external work and for heavily loaded floors. Skimming the back of each tile as well as combing the bed puts far more adhesive into the floor than the notch figure suggests.

How much coverage you actually need under the tile

BS 5385 is the British standard for wall and floor tiling, split into parts: Part 1 for internal wall tiling in dry conditions, Part 2 for external wall tiling, Part 3 for internal and external floor tiling, Part 4 for tiling in special conditions such as wet areas, and Part 5 for natural stone. It is what a specification will reference and what a dispute will be judged against.

The standard requires solid bedding rather than dabs, and it sets minimum contact between adhesive and tile. We could not verify the exact percentages against the standard itself, because BS 5385 is paywalled, and the secondary sources do not agree. Weber quote a minimum of 85% coverage on a wall in a dry area with 100% the ideal in wet areas and on floors. Other technical summaries quote 80% for dry internal work and 95% for wet areas and external work. The direction of travel is consistent even where the numbers are not.

The safe reading is the strict one. Aim for full contact on any floor, in any shower or wet room, on anything external and under any large format tile, and accept small voids only on a dry internal wall. Lift the first tile you lay and look at the back. If the ridges have not collapsed into a continuous bed, the notch is too small, the adhesive has skinned over or the background is too uneven, and all three are cheaper to fix in the first square metre than the last.

Grout is arithmetic, and so are movement joints

There is no such thing as a fixed coverage per bag of grout, because the volume you are filling depends on the tile as much as on the product. Mapei publish the calculation directly for Ultracolor Plus: tile length plus tile width, divided by length times width, multiplied by tile thickness, joint width and 1.6, giving kilograms per square metre with the dimensions in millimetres. A 300 x 300 x 10 mm tile at a 3 mm joint works out around 0.32 kg/m². The same tile at a 6 mm joint is double that. A 600 x 600 x 10 mm tile at 3 mm is nearer 0.16, because a larger tile has less joint per square metre.

Mapei's own printed table sits above what that formula produces, rounding up for mixing losses and the grout that never makes it into a joint, so it is sensible to work out the figure and then buy the next bag up. Ultracolor Plus is sold in 23 kg bags and in 5 kg and 1 kg boxes depending on colour, and is rated for joints from 2 to 20 mm, which covers essentially all domestic work.

The last thing to order, and the one people forget, is movement joints. BS 5385 asks for a perimeter joint on any tiled floor with a dimension over 2 m, intermediate joints dividing large floors into roughly square fields no greater than 10 m by 10 m, structural movement joints carried straight through the tiling, and, where there is underfloor heating, intermediate joints no more than 3.5 m apart. These are silicone or a proprietary profile rather than grout, and a heated floor grouted solid across a doorway will crack. Buy the profiles and matching silicone with the tile.

Adhesive and grout coverage

Adhesive figures are derived from Mapei's published consumption of 1.2 kg/m² per mm of bed thickness for Keraflex Maxi S1, using the rule that a square notch leaves a bed about half its depth. Grout figures are from Mapei's published formula for Ultracolor Plus. Both assume a flat background and no back-buttering.

Adhesive consumption of 1.2 kg/m² per mm of bed from the Mapei GB technical data sheet for Keraflex Maxi S1; notch size by tile size from Weber UK's guidance on using a notched trowel. Grout figures calculated with Mapei's published formula for Ultracolor Plus, (A+B)/(A×B) × C × D × 1.6. Mapei's own printed grout table runs above the formula result, so round up. The bed-depth-is-half-the-notch rule is trade practice, not a manufacturer figure.

What goes wrong ordering tile

Ordering square metres instead of boxes. Tile is supplied in boxes covering a fixed area, so what you buy is whole boxes. Apply the waste allowance first, then round up, and expect the real allowance to land above the nominal percentage.

Using one adhesive coverage figure for everything. At 1.2 kg/m² per mm of bed, a 20 kg bag reaches about 5.5 m² at a 3 mm bed and under 3 m² at 6 mm. Changing the trowel changes the bag count more than anything else you decide.

Dabbing instead of bedding solid. BS 5385 wants near-full contact under floors, wet areas and large formats. Dabs leave voids that crack the tile under load and hold water in a shower.

Buying grout on a remembered coverage. Consumption scales with joint width and tile thickness and falls as the tile gets bigger. The same tile at a 6 mm joint uses twice what it does at 3 mm, so run the numbers for your actual joint.

Leaving out movement joints. A perimeter joint is wanted on any floor over 2 m, intermediate joints on fields over 10 m, and joints no more than 3.5 m apart over underfloor heating. Grouting straight through is what cracks a heated floor.

Mixing batches. Shade varies between production runs. Order the full quantity at once, check batch codes on delivery, and keep a spare box, because the original batch will not be available later.

Frequently asked questions