Thinset Calculator

1. Measure your area. Multiply the length by the width of the floor or wall in feet to get the square footage. For an odd-shaped room, break it into rectangles and add them up, or type the total straight into the advanced Total area box.

2. Pick your tile size. The dropdown sets the recommended trowel notch and the coverage you get from one bag. Bigger tiles need a bigger notch, which spreads a thicker bed and covers fewer square feet per bag.

3. Read the result. The calculator adds a waste allowance, divides by the coverage per bag, and rounds up to whole 50 lb bags - because you can only buy full bags. Open More options to change units, bag size, waste, or add a price for a quick cost estimate.

Thinset (also called thin-set mortar) is the cement-based adhesive that bonds tile to a floor, wall, or backer board. Unlike paint, its coverage is driven almost entirely by the trowel you use, not the tile itself. A small V-notch trowel used for mosaics lays a thin ribbon and can stretch a 50 lb bag across roughly 100 square feet. A large square-notch trowel for 12-inch or bigger tile lays a much thicker bed, so the same bag might only cover 30 to 45 square feet.

That is why this thinset calculator asks for tile size: it maps your tile to a sensible trowel and a real-world coverage rate, then works backward from your square footage. Always round up. Running out mid-job means a hard stop, and a fresh batch rarely blends invisibly with a bucket that has already started to cure.

Bags = round up ( area x (1 + waste) / coverage per bag )

Where:
Area = length x width in square feet (or your Total area entry)
Waste = 10% by default, more for diagonal layouts and rooms with lots of cuts
Coverage per bag = square feet a full bag covers at the recommended trowel notch

Example: a 100 sq ft floor with 10% waste is 110 sq ft. At 85 sq ft per 50 lb bag for standard tile, that is 110 / 85 = 1.29, which rounds up to 2 bags.

Small bathroom floor, 5 ft x 8 ft (40 sq ft), standard tile: 40 x 1.10 = 44 sq ft / 85 = 0.52, so 1 bag covers it.

Kitchen floor, 12 ft x 15 ft (180 sq ft), 12-inch tile: at 45 sq ft per bag, 180 x 1.10 = 198 / 45 = 4.4, round up to 5 bags.

Shower wall in mosaic, 60 sq ft: at 100 sq ft per bag with a V-notch, 60 x 1.10 = 66 / 100 = 0.66, so 1 bag is plenty.

Buy one extra bag on big jobs. The coverage printed on the bag is a best case; uneven substrates soak up more.

Match the mortar to the tile. Large-format and heavy porcelain tile often call for a medium-bed or LFT mortar, which covers less per bag.

Back-butter big tiles. Spreading a skim coat on the back of 12-inch and larger tile improves the bond but uses more material, so lean toward the higher estimate.

Mix only what you can use. Thinset starts curing once wet and has a pot life of about two hours. Keep unopened bags dry and up off the floor.