Thinset Calculator

Thinset coverage depends on the notch, not on the tile colour. MAPEI Kerabond’s data sheet lists 6.97 to 8.36 square feet per 50 lb bag with a 1/4 inch square-notch trowel, and this page starts at the imperial coverage on the form, the low end of that row. A larger notch covers less floor per bag. The notch field is a label so you remember which row you typed. It does not look up a second chart on its own.

Thinset coverage is a function of the notch, the substrate, and the tile, which is why a single number would be a fiction. A 6 mm notch and a 12 mm notch do not move the same amount of mortar. The maker prints a coverage for each, often as a range. Type the figure that matches the notch you will hold and the tile size they name. The notch field on this form is there so the result remembers the choice. The unit test checks that two notches with the same coverage return the same bags. That is the point of the label.

Twelve square metres plus 10 percent is 13.2. A bag that covers 4 square metres is 3.3 bags, which rounds up to 4. If the bag covers 5 square metres at a smaller notch, type 5 and the count falls. Do not average a range. If the bag says 3 to 4 square metres, use the lower number when you would rather have a bag left, and say you did. Back-buttering large tile uses more thinset than the notch alone. If the instructions add that, reduce the coverage to what the instructions imply or add a second pass in waste. Do not invent the reduction.

Underlayment is a separate sheet count. Grout is the joint after the tile is down. Mortar for block is another coverage. None of those numbers belong in this field. There is no price per bag. Buy the same product the coverage came from, because a different polymer-modified bag is not the same yield.

Wall tile and floor tile can share the area maths and still need different notches. Run the page twice and label the results with the notch field. A heated floor or a membrane may have its own trowel requirement in the membrane instructions. Follow that requirement's coverage, not a default this page refused to store.

Area starts at 100 sq ft. Area to set in square feet. Trowel notch starts at 0.25 in. Notch size. 1/4 in matches the Kerabond coverage below in inches, or millimetres on the metric toggle. Waste allowance starts at 10 %. For ridges you scrape off and what is left in the bucket. Coverage per bag starts at 75 sq ft. 75 sq ft is about 6.97 m², the low end MAPEI prints for a 50 lb bag of Kerabond with a 1/4 in square-notch trowel (6.97–8.36 m²), checked 27 October 2026.

A worked notch makes the refusal obvious. Suppose the bag says a 6 mm square notch covers 5 square metres and a 10 mm notch covers 3. On 12 square metres with 10 percent waste the area is 13.2. The 6 mm notch is 13.2 divided by 5, which is 2.64, so 3 bags. The 10 mm notch is 13.2 divided by 3, which is 4.4, so 5 bags. You get that difference only by typing 5 or 3. The starting coverage is 6.97 square metres, the low end of the Kerabond 6 mm row. Replace it when the bag in front of you prints a different figure. Large-format tile often requires a larger notch and back-buttering. If the instructions say to back-butter, the coverage number you type should already include that extra mortar, or you should lower the coverage. The page will not guess the reduction. Mix only the bags you can use in the open time. A bag left to skin in the bucket is waste the percentage might cover, and a bag you mix tomorrow is another bag. Substrates that are not flat use more thinset in the low spots. That is a reason to raise waste, not a reason to invent a coverage chart. Underlayment boards change the area only if you are also bedding the board. Count that layer with its own coverage.