How Much Tile Adhesive Do I Need? UK Guide

Tile adhesive coverage is set by how thick a bed you lay, and that is controlled by the notched trowel you use. A small notch spreads a thin bed and covers a lot of area per bag; a big notch for floor tiles lays a thick bed and covers far less. As a working guide for a standard cement-based (powder) adhesive from a 20 kg bag: small wall tiles on a 6 mm notch cover about 5 m² per bag; medium wall tiles on an 8 mm notch cover about 3.5 m² per bag; floor tiles and porcelain on a solid 10 to 12 mm bed cover about 2.5 m² per bag; large-format tiles over 600 mm, back-buttered, cover about 2 m² per bag.

Ready-mixed tub adhesive is a different product: a 15 kg tub covers roughly 5 m² of small wall tiles, and it is only suitable for walls in dry or lightly wet areas, not floors or wet rooms. Every manufacturer prints a coverage figure per notch size on the bag — BAL, Mapei and Weber all do — so check yours, but the figures above are a safe planning start.

Takeaway: pick your coverage figure from the trowel notch, not just the area; walls at 6 mm cover roughly double what floors at 10 mm do.

This is the part that catches people out. Wall tiles are often fixed with a notched bed that leaves small ridges, which is fine for a wall. Floors are different: BS 5385-3, the code of practice for tiling floors, requires a solid bed with no voids under the tile, because a foot landing on a hollow spot cracks the tile. Achieving a solid bed usually means back-buttering the tile as well as notching the floor, and that roughly doubles adhesive use compared with the ridged, part-contact bed many people copy from wall tiling. So if you tiled a wall at 5 m² per bag, do not assume the floor will be the same — plan for around 2.5 m² per bag on a porcelain floor, less again for large format.

Takeaway: floors need a solid bed under BS 5385-3, so budget roughly half the coverage per bag that you would for walls.

Take a bathroom in a Manchester terrace: 12 m² of 300 by 600 mm ceramic wall tiles, and 6 m² of 600 by 600 mm porcelain floor tiles.

For the walls, medium tiles on an 8 mm notch cover about 3.5 m² per bag, so 12 divided by 3.5 = 3.4, which rounds up to 4 bags of 20 kg adhesive. For the floor, porcelain on a solid 10 mm bed covers about 2.5 m² per bag, so 6 divided by 2.5 = 2.4, rounding up to 3 bags. That is 7 bags of adhesive in total for the room. Buy the seventh bag even though the maths says 6.8 — an uneven floor or a couple of cuts that need re-buttering will use it, and a spare unopened bag goes back for a refund far more easily than a part-tiled floor waits for the shop to open.

For grout, large tiles use surprisingly little: 6 m² of 600 by 600 mm floor tiles at 3 mm joints works out at well under a kilo, so a single 5 kg bag covers it with room to spare. The 12 m² of 300 by 600 wall tiles at 2 mm joints is similar — one 5 kg bag of wall grout does the walls. Small mosaics are the opposite: dozens of joints per square metre can push grout use up tenfold, so never carry a large-tile grout figure over to mosaics.

Takeaway: this bathroom needs about 7 bags of adhesive and two 5 kg bags of grout; buy the extra adhesive bag rather than risk stopping mid-floor.

Grout quantity depends on the tile size, the joint width and the tile thickness. The thinner and larger the tile, and the narrower the joint, the less grout you use, because there is less joint volume to fill per square metre. As a rough guide, a 5 kg bag grouts around 5 to 10 m² of typical 300 by 600 wall tiles at 2 to 3 mm joints, but only 1 to 2 m² of small mosaics. If you want it exact, grout use per m² rises with (tile length + tile width) divided by (tile length x tile width), multiplied by the joint width and depth — which is the long way of saying small tiles with wide joints drink grout, and big tiles with fine joints barely touch it.

Takeaway: one 5 kg bag covers a small-to-medium tiled area at fine joints; size up sharply for mosaics or wide joints.

Here is the point the coverage tables on the back of the bag never make: the substrate decides how much you actually use, not the tile area. A flat, primed, plumb wall or a self-levelled floor will hit the bag's coverage figure. A wavy plastered wall or an old floor with dips will not, because you end up using the adhesive bed to take up the level as you go, laying it thicker in the low spots. On a genuinely uneven floor, adhesive use can run 30 to 50 percent over the flat-surface figure. That is why professional estimates always assume a bag or two over the clean calculation, and why levelling or priming the substrate first is not just about a good finish — it is what makes the coverage figure honest.

Takeaway: an uneven wall or floor can push adhesive use up by a third or more, so level and prime first and buy over the flat-surface figure.

In practice, a tiler mixes only what they can lay before it goes off — cement-based adhesive has a pot life of around half an hour, and a tub or bucket that starts to stiffen gets thrown, not watered down and stretched. They key or prime the substrate first, they solid-bed and back-butter floors and large format as a matter of course, and they buy from a proper tile merchant like Topps Tiles or Tile Giant, or from Screwfix or Wickes for a small job, keeping a spare bag in the van rather than the exact number. A 2026 price check puts a 20 kg bag of standard-set grey adhesive at roughly ten to fifteen pounds, so the spare bag is a few pounds against the cost of a stalled job.

Takeaway: mix in small batches, always solid-bed floors, and keep a spare bag — the maths gives the minimum, not the number to buy.

Use the Tile Calculator to work out how many tiles you need with wastage, then apply the coverage figures above for adhesive and grout. If you are levelling a floor first, the Screed Calculator sizes the screed, and the guide on how many tiles you need walks through the tile count itself.

Disclaimer: This guide is for planning. Actual adhesive and grout use depends on substrate flatness, trowel size, tile size, joint dimensions and the specific product. Always check the coverage figure on your bag and buy a little over.