How much tile adhesive do I need?
Adhesive is sold by the bag and used by the trowel, and the trowel is set by the tile. A 600 × 600 tile needs nearly four times the adhesive of a mosaic over the same floor — which is why “one bag does 5 m²” is right for one tile size and wrong for all the others.
Quick answer
Over 10 m² on a flat substrate, reckon on 3 bags of 20 kg for a 300 × 300 tile and 4 for a 600 × 600 — 44 kg and 66 kg respectively. The quantity is set by the trowel notch, which is set by the tile: 1.7 kg per m² at a 3 mm notch rising to 7.5 kg at 15 mm. One 20 kg bag therefore covers anywhere between 2.7 and 11.8 m². Add 20–40% on an uneven wall or an old screed. Grout runs the other way — the bigger the tile, the less of it.
| Tile size | Trowel notch | Adhesive | 20 kg bags | Grout |
|---|---|---|---|---|
| 50 × 50 mosaic | 3 mm | 18.7 kg | 1 | 19.4 kg |
| 100 × 100 | 6 mm | 33.0 kg | 2 | 10.1 kg |
| 150 × 150 | 6 mm | 33.0 kg | 2 | 6.8 kg |
| 200 × 200 | 8 mm | 44.0 kg | 3 | 5.2 kg |
| 300 × 300 | 8 mm | 44.0 kg | 3 | 3.5 kg |
| 250 × 400 | 10 mm | 55.0 kg | 3 | 3.4 kg |
| 200 × 500 | 10 mm | 55.0 kg | 3 | 3.6 kg |
| 300 × 600 | 10 mm | 55.0 kg | 3 | 2.6 kg |
| 450 × 450 | 10 mm | 55.0 kg | 3 | 2.3 kg |
| 600 × 600 | 12 mm | 66.0 kg | 4 | 1.7 kg |
| 200 × 1200 plank | 12 mm | 66.0 kg | 4 | 3.0 kg |
| 600 × 1200 | 15 mm | 82.5 kg | 5 | 1.3 kg |
Per square metre, that is 1.9 kg for a mosaic and 8.3 kg for a 600 × 1200 — a four-fold spread across sizes people choose from the same showroom.
The notch is the whole answer
Adhesive use is set by the depth of the bed, and the bed is set by the trowel's notch depth. The tile only enters the calculation because a bigger tile needs a deeper bed: it has further to span between high and low spots in the substrate, and more of its own weight to hold while it sets. Pick the notch and the quantity follows.
| Notch | kg per m² | Suits tiles up to |
|---|---|---|
| 3 mm | 1.7 | Mosaic and sheet-mounted |
| 6 mm | 3.0 | 150 mm equivalent side |
| 8 mm | 4.0 | 300 mm equivalent side |
| 10 mm | 5.0 | 450 mm — covers 300 × 600 |
| 12 mm | 6.0 | 700 mm — covers 600 × 600 |
| 15 mm | 7.5 | Larger, back-buttered |
Why the notch is keyed to the equivalent side, not the long edge
A 300 × 600 and a 600 × 600 have the same 600 mm long edge and want different trowels. Sizing off the longest edge gets every plank format wrong, because a plank is narrow enough to bed easily in one direction. What matters is the square root of the tile's area — its equivalent side. For 300 × 600 that is 424 mm, which falls in the 10 mm band; for 600 × 600 it is 600 mm, which falls in the 12 mm band. The calculator does this for you and shows which notch it picked.
What makes it worse than the table
- An uneven substrate. Every figure above assumes flat. On a wavy wall or an old screed, add 20–40% — the adhesive is filling the hollows as well as bedding the tile, and that is unbounded until you have actually looked at the floor with a straight edge. Levelling compound is cheaper than adhesive for that job.
- Back-buttering. Required by most large-format tile manufacturers and by any external or wet-area installation, and it roughly adds another 2–3 mm of bed. The 15 mm row already assumes it.
- Solid bed coverage. A floor needs the bed essentially void-free, and the usual specified minimum is 95% for wet areas and heavy traffic. Notched ridges that are not collapsed properly leave voids, and the fix on site is more adhesive.
- Thick-bed on a timber floor. Plywood overlay and a flexible adhesive change the figures. The adhesive's own data sheet governs.
Grout goes the other way
Grout volume comes from joint length, and joint length falls as tiles get bigger. Over the same 10 m², a mosaic swallows 19.4 kg while a 600 × 1200 takes 1.3 kg — a fifteen-fold difference in the opposite direction to the adhesive. A plank is the exception that proves the rule: 200 × 1200 takes more grout than a 600 × 600 because it has far more linear metres of joint for its area.
Grout also depends on joint width and tile thickness, which the table fixes at 3 mm and 10 mm. A 10 mm joint in a 20 mm porcelain is a different order of quantity altogether — both terms are multipliers, so it is roughly six times the figure above, not twice. Switching to epoxy barely moves the weight: at 1.55 against 1.6 g/cm³ it is marginally lighter for the same joint, and the reason to use it is chemical resistance, not quantity.
Common questions
Should I buy ready-mixed or powdered adhesive?
Powder for floors and for anything large-format or wet, because cement-based adhesive sets by hydration and reaches full strength regardless of depth. Ready-mixed sets by drying, so it needs air to get at it — it is for small wall tiles in dry areas, and it will never properly harden under a large tile. The quantities above are for powder; ready-mixed is sold by volume in tubs and its own tub states its coverage.
How much does one 20 kg bag actually cover?
Between 2.7 and 11.8 m² depending entirely on the notch: 11.8 m² at a 3 mm notch, 5.0 m² at 8 mm, 4.0 m² at 10 mm, 3.3 m² at 12 mm and 2.7 m² at 15 mm. Any single coverage figure printed on a bag is quoting one notch, and it is usually not the one your tile needs.
Can I buy exactly what the calculator says?
Buy one bag more than you need on anything over about 15 m². Adhesive has a pot life of 20–40 minutes once mixed, so a batch that goes off while you are cutting is simply gone, and a part-used bag that has been open in a damp garage is also gone. Unopened bags normally go back.
Does the figure change for wall versus floor?
Not the notch arithmetic, but the practice around it does. Walls take smaller tiles and so less adhesive per square metre; floors are where solid bed coverage matters most, and where the manufacturer's minimum coverage percentage is usually specified. Floors also carry the tile's weight in shear rather than hanging it, which is why a floor adhesive and a wall adhesive are not interchangeable.
Related
- Tile calculator — your room and your tile, with the notch, the adhesive and the grout worked out together
- Adhesive and grout coverage reference — the full tables and where each figure comes from
- How many tiles do I need? — the tile count itself, by size and layout
- A real bathroom, start to finish
- These tables as JSON — with the inputs that produced each row
Last reviewed 2026-10-17. Quantities generated from the tile calculator on this site; a test re-checks every figure above against the live tool on each build.
Sources and confidence
Every figure used on this page, what kind of figure it is, and where it came from. Figures marked as working estimates have no single authority behind them — they are the ones to check against your own supplier.
| Figure | Kind | Source | Note |
|---|---|---|---|
| Every adhesive and grout quantity in the tables | Derived | Generated from this site's tile calculator | Produced by driving the calculator across the tile sizes and notches listed. A test re-checks each cell against the live tool on every build. |
| Notch keyed to the tile's equivalent side | Derived | Geometry | The square root of the tile's area. Keying off the longest edge alone gets every plank format wrong. |
| kg per m² by trowel notch | Working estimate | no primary source consulted | Trade practice, flat substrate. Adhesive manufacturers publish their own coverage and theirs governs; see the adhesive and grout coverage reference. |
| Grout density, 1.6 g/cm³ cement-based and 1.55 epoxy | Working estimate | no primary source consulted | Typical values. A specific product's data sheet will differ slightly. |
| 20–40% more on an uneven substrate; 95% bed coverage for wet areas | Working estimate | no primary source consulted | Trade practice. The true figure depends on how far out of flat the substrate is, which no calculator can see. |
Derived Calculated from geometry. The formula is on this page. Published From a manufacturer data sheet or published standard, cited below. Working estimate Trade practice, rounded up. No single authority; the weakest category here.