Thinset Mortar Calculator
Calculate how many bags of thinset mortar you need to set tile, based on area and trowel notch size.
Coverage shown for small to large-format tile.
Thinset is the cement-based mortar that bonds tile to the floor or wall, and how much you need depends far more on the trowel than on the tile itself. The notched trowel you spread it with sets the ridge height, and bigger notches lay down more mortar per square foot, so coverage per bag drops sharply as the notch grows.
A standard 50-pound bag covers a wide range depending on that notch. A small quarter-inch square notch, used for mosaics and small tile, can stretch to roughly 90 square feet, while a half-inch notch for larger floor tile covers closer to 50, and the big three-quarter-inch notches used for large-format tile cover only 30 to 40. Pick the coverage that matches your trowel and tile size, divide your area by it, and round up to whole bags.
A few things push usage higher than the chart suggests. An uneven or rough substrate swallows extra mortar as you fill low spots, large and heavy tiles need full coverage with back-buttering, and any mortar that skins over before you set tile into it is wasted. Mix only what you can use in about 20 to 30 minutes, because thinset starts curing in the bucket and cannot be brought back with more water once it stiffens. Always buy one bag more than the math says, since running out mid-job means a seam where the batches meet.