Tile Adhesive Calculator

How much tile adhesive do I need?

Adhesive quantity comes from the area and the thickness of the bed, and the bed thickness is set by the trowel. A notched trowel spreads ridges that collapse to about half the notch depth when the tile is pressed down: a 6 mm notch leaves a bed of roughly 3 mm, a 10 mm notch about 5 mm, and a 12 mm notch about 6 mm. Powder adhesive weighs about 1.3 kg for every square metre at one millimetre thick, so the coverage figures on data sheets follow directly: 4 kg/m² for walls on a 6 mm trowel, 6.5 kg/m² for floors on a 10 mm trowel, 8 kg/m² for back-buttered large format.

The calculator uses those typical figures, or the exact coverage printed on your bag if you enter it, and adds 10% for what stays in the bucket, what gets combed off the edges and what a slightly uneven floor absorbs. Then it rounds up to whole bags or tubs, because a merchant will not sell you 4.3 bags.

The formula

Adhesive coverage by trowel

Ready-mixed adhesive is lighter per square metre because it is sold wet and is combed thinner. It is not a like-for-like coverage comparison with powder, which is why the calculator treats it as its own option.

Worked example

A 4 m × 3 m kitchen floor = 12 m² of 600 x 600 mm porcelain. Floor tiles go down on a 10 mm notched trowel, which gives a bed of about 5 mm, and at 1.3 kg/m² per millimetre that is 6.5 kg/m².

Net adhesive = 12 × 6.5 = 78 kg. Add the 10% allowance = 85.8 kg. In 20 kg bags: 85.8 ÷ 20 = 4.29, rounded up to 5 bags. Each bag covers about 3.1 m² at this bed, and you will have roughly 14 kg spare, which is the right amount to have when a corner of the floor turns out to be lower than the rest.

The same floor with the tiles back-buttered on a 12 mm trowel needs 8 kg/m², so 105.6 kg and 6 bags. On a wall with 6 mm trowel it would need only 4 kg/m², 52.8 kg and 3 bags.

Powder or ready-mixed?

• Cement-based powder sets by chemical reaction, so it cures under a tile and in a wet room. Use it for every floor, every shower, every large tile and anything outside. Flexible (S1) grades are needed over underfloor heating, timber floors and plywood.
• Ready-mixed tubs set by drying, so they only work where air can reach the adhesive: small ceramic tiles on a dry wall. Under a 600 mm porcelain tile the middle never dries, and the tile falls off months later.
• Rapid-set powder uses the same coverage but has a pot life of 30 to 45 minutes. Mix half bags at a time until you know your speed.
• White or grey: the coverage is identical. Use white under natural stone, glass and translucent tiles, where grey shows through.

What else the job needs

• The tiles themselves, with the right cutting allowance for the layout: the tile calculator works from the same room size.
• Grout, worked out from the tile size and joint width in the grout calculator. Adhesive and grout are separate products; the adhesive coverage above does not include the joints.
• Silicone for every internal corner and the junction with the bath or worktop. A 310 ml cartridge gives roughly 12 to 15 m of a 6 mm bead, so one is usually enough for a shower and two for a full bathroom.
• Primer for plaster, plasterboard, anhydrite screed and any dusty surface, plus a decoupling mat or tanking where the substrate calls for it.
• For an odd-shaped room, get the area from the area calculator and use the "I already know the area" mode.

Mistakes that cost you a bag

• Using a small-notch trowel on a floor to save adhesive. The bed ends up hollow, the tile sounds drummy, and it cracks the first time something is dropped on it.
• Skimming an uneven floor with adhesive instead of levelling compound. Every extra millimetre is 1.3 kg/m², and thick beds shrink and crack anyway.
• Mixing a whole 20 kg bag when you can only lay 2 m² an hour. Adhesive that has started to set cannot be revived with water.
• Forgetting that back-buttering doubles the pass. Large format tiles need a thin coat on the tile as well as the combed bed on the floor.

Planning your order

Check the inputs before buying: measure the surfaces you need, then apply an allowance and round to whole packs. The guides include worked examples you can follow alongside this calculator.