A 20kg bag of cement-based tile adhesive covers roughly 6–7.5 m² with a 6mm notched trowel and 4–5 m² with a 10mm trowel (Mapei). On walls with smaller tiles a bag can stretch to 8–10 m². On floors and large-format tiles it can drop to around 4 m².
As a rule of thumb, allow about 2.5–3 kg per m² for standard wall tiles and 4–5 kg per m² for floors and large format.
There's no single answer, because coverage depends on the trowel, the tile and what you're sticking it to. But the manufacturers publish figures, and they're close enough to plan a job and order the right number of bags.
20kg bag coverage by trowel size
The trowel notch decides how thick the bed is, and that decides how far a bag goes. Mapei's figures for a standard cement-based adhesive:
| Trowel (square notch) | Adhesive per m² | One 20kg bag covers |
|---|---|---|
| 6mm | about 2.7–3.3 kg | 6–7.5 m² |
| 10mm | about 4–5 kg | 4–5 m² |
Walls vs floors
Walls usually take less adhesive than floors, because wall tiles are smaller and lighter and go on with a smaller notch. As an example, a UK retailer listing for BAL Flex One gives these approximate figures for one 20kg bag:
| Where | One 20kg bag covers | Works out at |
|---|---|---|
| Dry wall | about 10 m² | about 2 kg/m² |
| Wet wall | about 8 m² | about 2.5 kg/m² |
| Floor | about 5.3 m² | about 3.8 kg/m² |
Wet walls take more because you want full coverage behind every tile, with no voids for water to sit in.
Large-format tiles
Large-format tiles need a thicker, fuller bed, and usually back-buttering too. Mapei gives large-format adhesive use by bed thickness: about 1.2 kg per m² for every mm of bed.
| Bed thickness | Adhesive per m² | One 20kg bag covers |
|---|---|---|
| 3mm | about 3.6 kg | about 5.5 m² |
| 4mm | about 4.8 kg | about 4 m² |
| 6mm | about 7.2 kg | under 3 m² |
Different products vary. A retailer listing for Ultra Tile ProFlex SP, for example, gives 4.5 kg/m² at a 3mm bed, or about 4.4 m² per 20kg bag. Always check the data sheet for the adhesive you're using.
What makes a bag go further or run out sooner
- Uneven walls and floors soak up far more adhesive. Level or board out first. It's usually cheaper than filling hollows with adhesive.
- Back-buttering large or heavy tiles adds roughly another millimetre of bed.
- Textured or ribbed tile backs take more to fill.
- Solid bed for showers and external floors uses more than a standard notched bed.
- Mixing more than you can use before it goes off. Rapid-set adhesives give you less working time.
Lift a tile early on to check you're getting full coverage. If you're not, go up a trowel size rather than pressing harder.
Worked examples
Bathroom walls
20 m² of 300×600mm wall tiles in a shower area, at about 2.5–3 kg/m²: 20 × 3 = 60 kg. Order 3 bags, or 4 if the walls are out of true.
Kitchen floor
12 m² of 600×600mm porcelain with a 10mm trowel, at about 5 kg/m²: 12 × 5 = 60 kg. Order 3 bags, plus a fourth if you're back-buttering.
For a whole job, the free tiling calculator works out adhesive, grout and tiles together. The floor and wall calculators work it out from the room size. For wastage, grout and trims, see how much tile and materials to order.
Sources
- Mapei Adesilex P9 technical data sheet · consumption per m² and coverage per 20kg bag by trowel size
- Mapei Large Format Tile Adhesive technical data sheet · 1.2 kg/m² per mm of bed thickness
- Craven Dunnill: BAL Flex One 20kg · retailer listing; approx. coverage per bag on dry walls, wet walls and floors
- The Underfloor Heating Store: Ultra Tile ProFlex SP 20kg · retailer listing; 4.5 kg/m² at a 3mm bed
Prices change. Figures were checked on 24 October 2026; always check current costs and your own figures before quoting.