How the tile adhesive calculator works
The amount of adhesive under a tile is set by the trowel, not by the tile. A square-notched trowel leaves ridges whose height equals the notch; when the tile is pressed down, the ridges collapse into a bed roughly half as thick. So each notch size corresponds to a fairly predictable consumption of powder per square metre, which is what adhesive manufacturers print in their technical sheets.
Adhesive = area × (notch rate + 1.3 kg/m² if back-buttered) × 1.10Rates used, for standard cement-based (C1/C2 type) powder: 2.5 kg/m² for a 6 mm notch, 3.2 for 8 mm, 4.0 for 10 mm and 5.0 for 12 mm. Back-buttering, a 1 mm skim scraped on the back of each tile, adds about 1.3 kg/m². The 10% covers adhesive that skins over on the board and what is scraped off at joints and edges. Square feet are converted to square metres, and kilograms to pounds (1 lb = 0.4536 kg).
Worked example
A 12 m² kitchen floor in 45 × 45 cm porcelain is laid with a 10 mm notch and back-buttered, as recommended for tiles of that size. The rate is 4.0 + 1.3 = 5.3 kg/m², so 12 × 5.3 = 63.6 kg, or 69.96 kg with the allowance. Three 25 kg bags (75 kg) cover it; 20 kg bags would take four. In the US, 130 ft² of 12 × 24 in tile with a 1/2 in notch and back-buttering is about 12.1 m² × 6.3 × 1.1 = 83.7 kg, or 185 lb: four 50 lb bags.
Notch size, tile size and coverage
| Notch | Typical tile size | Consumption | One 25 kg bag covers | One 50 lb bag covers |
|---|---|---|---|---|
| 6 mm (1/4 in) | Wall tiles up to 20 cm (8 in) | 2.5 kg/m² (0.51 lb/ft²) | 10 m² | about 98 ft² |
| 8 mm (5/16 in) | 20–30 cm (8–12 in) | 3.2 kg/m² (0.66 lb/ft²) | 7.8 m² | about 75 ft² |
| 10 mm (3/8 in) | 30–45 cm (12–18 in) | 4.0 kg/m² (0.82 lb/ft²) | 6.3 m² | about 60 ft² |
| 12 mm (1/2 in) | 60 cm (24 in) and larger | 5.0 kg/m² (1.02 lb/ft²) | 5 m² | about 49 ft² |
Coverage per bag is before the 10% allowance. Rapid-set, lightweight and flexible adhesives can differ by 20% or more, so compare with the consumption table on your bag.
Getting full coverage under the tile
- Aim for contact, not quantity. Floors and wet areas need close to full contact under every tile. Lift a tile now and then: if the ridges have not collapsed, the notch is too small or the adhesive has skinned.
- Comb in one direction. Straight, parallel ridges let air escape as the tile is pressed and slid; swirls trap voids.
- Back-butter large formats. Tiles over about 30 cm (12 in) and anything with a ribbed back need a skim on the back, which is why this option exists.
- Mix only what you can use. Most mixed adhesive stays workable for 2–4 hours in the bucket but only 20–30 minutes once combed on the substrate.
- Prime first. Absorbent screed or gypsum substrates need the primer the adhesive maker specifies, otherwise the bed dries out before it bonds.
Frequently asked questions
How much tile adhesive do I need per m2?
Roughly 2.5 kg/m² with a 6 mm notch, 3.2 kg with 8 mm, 4 kg with 10 mm and 5 kg with 12 mm, plus about 1.3 kg/m² if you back-butter the tiles.
How many square feet does a 50 lb bag of thinset cover?
About 98 ft² with a 1/4 × 1/4 in notch, 60 ft² with 3/8 in and 45 to 50 ft² with a 1/2 in notch, before waste.
How many bags of tile adhesive for 10 m2?
With an 8 mm notch you need about 35 kg including 10%, so two 20 or 25 kg bags; with a 12 mm notch and back-buttering it is about 70 kg, three 25 kg bags.
What size trowel for 60x60 tiles?
A 12 mm (1/2 in) square or slant notch, combined with back-buttering, is the usual choice for 60 × 60 cm (24 × 24 in) floor tiles.
Is back-buttering necessary?
It is strongly recommended for large-format tiles, natural stone, tiles with deep back ribs, and outdoor or wet floors, where hollow spots lead to cracks.
Last reviewed: 2026-09-27 · How we calculate