The size of the tile determines the choice of trowel. Large format tiles (where any side is larger than 15" [38.1 cm]) require a square-notch trowel with deeper notches like 1/2" x 1/2" x 1/2" (12 x 12 x 12 mm). Smaller sizes can be installed with a 1/4" x 1/4" x 1/4" (6 x 6 x 6 mm), or 1/4" x 3/8" x 1/4" (6 x 10 x 6 mm), square-notch trowel.