How much extra tile to buy

The usual way: divide the wall area by the tile area and add 10 %. Sometimes that leaves plenty spare, sometimes you are two tiles short and the showroom no longer has that batch. Counting from the layout is more accurate.

Why area is misleading

Area does not know how the tiles will fall. If a 450 mm strip remains at the wall with 600 mm tiles, every cut tile throws away 150 mm that cannot be used anywhere. If the strip is 200 mm, one tile gives three strips and there is almost no waste. Two bathrooms of the same area can need different amounts of tile.

How to count from the layout

1. Lay out the tiles on every wall and the floor from the chosen starting point.
2. Count the full tiles.
3. Count the cuts and see which of them can come from offcuts of other cuts. The blade takes 1–3 mm, and with patterned tiles the direction matters.
4. Add an overage for breakage by laying pattern (table below).
5. Round up to whole boxes.

Overage by laying pattern

The overage is added to tiles and cuts already counted, not to the area. That is why it is lower than the usual 10–15 %: the cuts are already counted honestly.

Example

Bathroom floor 1600×2100 mm, 600×600 mm tile, 2 mm joint, straight lay from a corner.

• full tiles: 2 × 3 = 6;
• a strip about 400 mm wide along the long wall: 3 tiles, the remaining 200 mm of each is no use;
• a strip about 300 mm high along the short wall: one tile gives two strips;
• the corner piece, about 400×300 mm: one more tile;
• 11 tiles in total, plus 5 % gives 11.55, so 12 tiles;
• 4 tiles per box (1.44 m²), so 3 boxes.

By area you would get 3.36 m² / 0.36 m² = 9.3 tiles, about 10.3 with 10 %, so 11 tiles and also 3 boxes. Here the two methods agree, but on walls with openings, niches and boxing the difference easily reaches a whole box.

What else changes the quantity

• The starting point. Moving it by half a tile changes every cut; see how to avoid thin tile slivers.
• The tile design. With multi-face tiles and marble with directional veining, offcuts cannot be used everywhere.
• Large formats. 1200×600 and up break more often when cut; keep the overage closer to 10 %.