Calculate floor area, account for cuts and breakage, and round up to full tile boxes.
Ordering tiles is easier when you know the room area, tile size, and how much material to reserve for cuts. A small allowance also helps if a tile cracks during installation or a matching replacement is needed later.
For a rectangular room, multiply its length by its width. Split an L-shaped room into rectangles, calculate each section, then add the areas. Measure in one unit throughout and subtract large areas that will not be tiled.
Multiply the tile length by its width, using the same units as the room. A 30 cm by 60 cm tile covers 0.18 m². For a 3.6 m by 4.2 m floor, the 15.12 m² area takes 84 tiles before allowing for cuts.
A straight, simple layout often needs about 10% extra; diagonal patterns, many corners, or large tiles in a small room can require more. In the example, adding 10% brings 84 tiles to about 93. If boxes contain eight tiles, round up to 12 full boxes. Check the packaging and keep spare tiles from the same batch.