Tile calculator — tiles, adhesive and grout

Divide the area by the area of one tile and add a waste margin: number of tiles = area × (1 + waste) ÷ tile area, rounded up. A 130 sq ft bathroom floor with 12 × 12 in tiles (1 sq ft per tile) and 10% waste comes to 130 × 1.1 ÷ 1 = 143 tiles. The same math works in metric with m² and tile dimensions in centimeters.

The waste goes into cuts at walls, pipes and corners — and the occasional tile that cracks. Diagonal layouts and patterns make every cut unique, pushing waste toward 15%. Tiles are sold by the box, so round up to whole boxes and check that every box carries the same shade number.

Thinset consumption is set by the trowel: a 1/4 in (6 mm) notch uses roughly 2.5 kg/m² and suits tiles under 12 in, while a 3/8 in (10 mm) notch uses roughly 4 kg/m² and is used for larger formats. The calculator converts that into whole bags so you know what to order.

Large-format tiles (from 12 in / 30 cm) should be back-buttered: comb mortar onto both the substrate and the back of the tile so coverage is complete. Full coverage matters most on floors and outdoors — voids behind the tile collect water, which can freeze and pop the tile loose, and hollow spots crack under load. In wet areas, always follow your local waterproofing standards before any tile goes on the wall.