What this calculator works out
Counting tiles is only half of a tiling shopping list. Once the tile count is settled, sticking them down and filling the joints between them both take a separate product, in a separate quantity, worked out from a separate set of numbers. This calculator picks up exactly where a tile count leaves off: enter the area, the tile's size and thickness, and whether it's going on a wall or a floor, and it works out the powdered or ready-mixed adhesive to buy, the grout to fill the joints, and turns both into bags, tubs and boxes rather than a bare weight nobody buys in.
This isn't a tile-count tool; for how many tiles and boxes a floor needs from its size, tile size and grout gap, see the Tile Calculator. The two pages share the same area and use broadly the same idea of a joint between tiles, but they answer different questions, one in tiles, this one in kilograms of adhesive and grout.
How the maths works
Adhesive is the simpler of the two: a coverage rate, in kilograms per square metre, multiplied by the area. That rate depends mainly on the trowel notch a tiler combs it out with, which in turn depends on whether it's going on a wall or a floor. Walls are usually spread with a smaller notch, commonly around 6mm, since the tile only has to be held rather than support foot traffic; floors need a deeper bed for full, even contact and are usually combed with a 10 to 12mm notch. This calculator uses 2.5 kg per m² for a wall and 4.5 kg per m² for a floor, cross-checked against Mapei Keraflex, BAL Flex One and Dunlop CS1-12/CX-24 coverage figures for their equivalent notch sizes; see the sources note below for the exact figures those come from.
Grout works differently, because it isn't spread evenly across the tile, it only fills the joints between them, so the sum has to work out how much joint there actually is. The trade convention for that, the same one behind Mapei's own published grout formula, treats each tile as "owning" a joint running along two of its own edges, works out the volume of grout that joint holds, and converts that volume to a weight using the grout's density.
Working the default example through: a 10 m² floor in 600 × 600mm tiles, 10mm thick, at a 3mm joint. Adhesive first: 10 m² × 4.5 kg/m² is 45 kg, plus 10% contingency is 49.5 kg, which needs 3 twenty-kilogram bags (60 kg bought). Grout: (600 + 600) ÷ (600 × 600) is 0.003333 per mm, × 10mm thickness is 0.03333, × 3mm joint width is 0.1, × 1.6 kg/L density is 0.16 kg per m²; × 10 m² is 1.6 kg, plus 10% contingency is 1.76 kg, which needs one 2.5kg box. That small grout figure isn't a mistake: a 600 × 600mm tile has far less joint length per square metre than a small tile does, which is exactly why large-format floors use noticeably less grout than a small-tile bathroom at the same joint width, the same relationship the Tile Calculator's own copy describes from the tile-count side.
Wall or floor, and choosing a trowel notch
The wall/floor toggle above changes two things at once: the adhesive coverage rate, since a wall's thinner bed uses noticeably less material per square metre than a floor's, and which adhesive forms are offered, since ready-mixed paste is a wall-only product here. Neither figure is a trowel-size input in its own right, because most domestic tilers pick a notch by the job type rather than the millimetre, a fine notch for small wall tiles, a coarser one for a floor, so the calculator bakes in a typical notch for each rather than asking for one directly. A tiler working from a manufacturer's own coverage table for a specific notch size can treat this calculator's kilogram figure as a cross-check rather than gospel; real coverage moves with substrate flatness, tile size and how generously a trowel is loaded, by a reasonable margin either way.
Large-format tiles, roughly 600mm and up on either side, usually need back-buttering as well as a floor-combed bed, spreading a thin layer of adhesive onto the tile itself before it goes down, to guarantee full contact underneath with no hollow spots. That extra step uses more adhesive than this calculator's flat per-square-metre rate assumes, so add a modest allowance, 10 to 20%, on top of the contingency toggle for a large-format job.
Powdered adhesive or ready-mixed paste
Powdered adhesive, mixed with water on site, is the default for most jobs, in 20kg bags, and is the only option this calculator offers for a floor: it cures to a harder, load-bearing bed that's rated for foot traffic and, in a flexible formulation, for underfloor heating and larger tiles. Ready-mixed adhesive, sold ready to trowel straight from a 15kg tub, at around 2.5 kg per m² on a typical 5mm notch, suits smaller ceramic wall tiles in a dry room, and its main selling point is convenience, no mixing, no waste from a part-used bag going off before the next job. It isn't generally rated for floors, for large or heavy tiles, or for a shower or other continuously wet area, which is why switching the surface toggle to floor above hides it and moves the calculation to powdered adhesive automatically.
A worked example, in UK prices, and a US aside
A small bathroom floor, 4m by 2.5m, in 300 × 300mm porcelain tiles 8mm thick, a 3mm joint, contingency on: 10 m² at the floor rate of 4.5 kg/m² is 45 kg, plus 10% is 49.5 kg, 3 bags of 20kg powdered adhesive. Grout: (300 + 300) ÷ (300 × 300) is 0.006667, × 8mm thickness is 0.05333, × 3mm joint is 0.16, × 1.6 kg/L is 0.256 kg/m²; × 10 m² is 2.56 kg, plus 10% is 2.816 kg, 2 boxes of 2.5kg (5 kg bought), noticeably more than the 600 × 600mm example above at the same area and joint width, purely because a smaller tile has more joint per square metre. At around £13 a bag and £9 a 2.5kg grout box, that's roughly £39 of adhesive and £18 of grout, call it £57 before trowels, spacers or a primer.
The US doesn't buy tile adhesive by the 20kg bag or the 15kg tub; the nearest equivalent is thinset mortar, sold in roughly 50lb (about 22.7kg) bags, such as Custom Building Products VersaBond or Mapei Ultraflex, spread with a 1/4in x 1/4in trowel for smaller tile through a 1/2in x 1/2in trowel for large format, and each product publishes its own coverage chart by trowel size rather than a flat kg/m² figure. US grout is typically bought by the pound in smaller boxes, 7lb, 10lb or 25lb being common, again with the manufacturer's own coverage guide for the joint width and tile size in question. Treat the area and joint width worked out above as the numbers to carry across to whichever US product's own chart applies, rather than expecting this calculator's kilogram figures or bag counts to translate directly.
Questions people ask
Powdered adhesive or ready-mixed?
Powdered, mixed with water, is the stronger, more load-bearing option and the only one this calculator offers for floors; it's also usually cheaper by the square metre. Ready-mixed paste, sold ready to use in a tub, suits smaller ceramic wall tiles in a dry room and saves the mixing step, but it isn't generally rated for floors, large or heavy tiles, or continuously wet areas such as inside a shower.
What trowel notch size should I use?
As a starting point, a 6mm notched trowel suits most wall tiles, and a 10 to 12mm notch suits most floor tiles, with a bigger notch again for large-format tiles that also need back-buttering. The tile manufacturer's own fitting guidance, and the adhesive's own coverage chart for that notch, should win over a general rule whenever the two disagree.
When do I need a flexible adhesive?
Flexible (often labelled S1) adhesive copes with more movement than a standard formulation, so it's the usual choice over underfloor heating, on a timber or plywood substrate that flexes slightly, for large-format tiles, and outdoors where temperature swings expand and contract the substrate. A standard, rigid adhesive is normally fine on a stable masonry or screeded background with ordinary-sized tiles.
How long before I can grout?
Most standard adhesives are ready to grout after roughly 12 to 24 hours; fast-set formulations can be ready in as little as 1 to 3 hours. Always check the specific product's own data sheet, since curing time depends on temperature, humidity and how thick the bed is, and grouting too early can disturb tiles that haven't fully gripped yet.
Why doesn't this calculator tell me how many tiles to buy?
Because that's a different sum, based on the tile's face size plus the grout gap rather than a coverage rate or a joint-volume formula. The Tile Calculator handles that half of the job; bring its area figure back here once the tile count and box quantity are settled, to work out what sticks them down and fills the joints.
How much contingency should I add?
10%, the default here, is a reasonable allowance for ordinary mixing waste and a bit left in the bucket on both adhesive and grout. Add more for a large-format job that needs back-buttering, since that uses noticeably more adhesive than a flat per-square-metre rate assumes, or for an uneven substrate that drinks more adhesive than a flat, well-prepared one.
Adhesive coverage figures are cross-checked against Mapei Keraflex, BAL Flex One and Dunlop CS1-12/CX-24 product data for their equivalent wall and floor notch sizes, and MapeStik ready-mixed adhesive for the tub coverage. The grout formula follows the standard trade convention behind Mapei's own published grout calculator; the 1.6 kg/L density figure is verified by working it back out of BAL Micromax2's own published coverage table (a cementitious grout typically falls in a 1.6 to 1.8 kg/L range, more flexible or polymer-modified products running towards the higher end). Real coverage varies with substrate flatness, tile size and application technique, so treat this as a planning estimate and round up when buying.