What this answers
How many tiles to buy for a floor or a wall, and how much grout to mix. You give the area (or the room’s two measurements), the size of one tile, the joint between tiles and how much extra you want for cuts and breakage. The page counts whole tiles, rounds up to whole packs if you give the pack size, and works out the volume of grout the joints need.
The count
Each tile owns a cell: the tile plus one joint in each direction. The area, with waste added, is divided by the cell and rounded up.
Cell = (tile width + joint) · (tile length + joint)
Tiles = (area · (1 + waste)) / cell, rounded up
The waste is yours to choose. A plain straight pattern in a rectangular room needs little; a diagonal pattern or a room with many corners usually needs more. The page opens on 10% as an example.
The grout
The joints are a trench of known width and depth. For tiles of width W and length L (millimetres), the grout in litres per square metre is
Grout = (W + L) / (W · L) · joint · thickness
The depth is the tile’s thickness. Turning litres into kilograms needs the grout’s density, which is on its datasheet; type it in and the kilograms appear.
Worked example
A 4 × 3 m floor, 30 × 30 cm tiles, 3 mm joints, 10% waste:
- the area is 12 m², and with waste 13.2 m²
- a cell is 303 × 303 mm = 0.0918 m², so 13.2 / 0.0918 = 143.8, rounded up to 144 tiles
- the joints take 0.16 litre per m² with 8 mm thick tiles: 12 · 0.16 = 1.92 litres
If the tiles come 1.44 m² to a pack, 13.2 / 1.44 = 9.2 gives 10 packs.
What is not included
- Openings. A door or a bath is not taken off. Type the area you tile if you want that.
- Adhesive, primer and waterproofing. They are sold by their own consumption figures, on the pack.
- Cutting at the walls. The count is by area. A room with lots of cutting can need more than the waste you give.
Common questions
Why are packs and kilograms empty?
They come from numbers on the box and the datasheet, and they differ between products. Type them and the
rows fill in.
What joint width should I use?
That is for you and the tile’s maker to decide. The 3 mm on the page is an example so that the
arithmetic can be checked.