How to use it
- Measure each room and type it as length × width, one room per line.
- Enter the tile size, the joint width and the tile thickness from the packaging and the spacers you plan to use.
- Choose the Laying pattern. Leave Waste empty to use its allowance, or type your own figure.
- Enter the Box size and the adhesive and grout figures from their data sheets, then read Boxes to buy.
How the tiles are counted
The room areas are added up, and the waste allowance is added on top. Each tile covers its own size plus the joint around it, so the number of tiles is the area with waste divided by that covered area, rounded up.
The boxes follow from the same area, or from the tile count when the box is counted in tiles, again rounded up to whole boxes.
tiles = area × (1 + waste) ÷ [(tile length + joint) × (tile width + joint)]
boxes = area × (1 + waste) ÷ box size (rounded up)Adhesive and grout
Adhesive is worked out per square metre of the laid area, using the consumption printed on the adhesive's data sheet for your notch size and tile size. The 4 kg per square metre in the form is only an example, and it is the number to replace.
The grout fills the joints. Each tile has joints of total length (length + width) along its edges, so the joints take (length + width) ÷ (length × width) × joint width × depth per square metre. Multiply by the grout density to get kilograms.
grout (kg per m²) = (L + W) ÷ (L × W) × J × D × density
L, W tile length and width (mm)
J joint width (mm)
D tile thickness, the depth of the joint (mm)What this calculator does not include
- Skirting, trims, threshold strips and the tiles lost to a broken tile in storage: add a spare box if you may need repairs later.
- Pattern matching between boxes. Buy all the boxes from one batch, because colour can change between batches.
- Underfloor heating mats, primers and the waterproofing membrane in wet rooms.
Worked example: a room of 4 × 3 m and a corner of 2.5 × 2 m
The two rectangles give 12.00 + 5.00 = 17.00 m². With the straight-laying allowance of 10 % the area to buy for is 18.70 m².
A 60 × 30 cm tile with a 3 mm joint covers (600 + 3) × (300 + 3) mm = 0.1827 m², so 18.70 ÷ 0.1827 gives 103 tiles. With 1.44 m² in a box, 18.70 ÷ 1.44 gives 13 boxes.
The adhesive is 17.00 × 4 = 68.00 kg. The grout is 0.192 kg per m² for an 8 mm deep joint with a 1.6 kg per litre density, so 17.00 × 0.192 = 3.26 kg.
| Straight (10 %) | Diagonal (15 %) | |
|---|---|---|
| Area to buy for | 18.70 m² | 19.55 m² |
| Tiles | 103 | 108 |
| Boxes of 1.44 m² | 13 | 14 |
Frequently asked questions
How much waste should I add for tiles?
For straight laying, 10 % is a common allowance for a rectangular room. Diagonal and herringbone laying need 15 % and 20 % because more tiles are cut and the offcuts cannot be reused.
Should I count the joints when I work out the number of tiles?
Yes. This calculator covers each tile with its joint, so the count is a little lower than for the tile alone. The difference is small for a 3 mm joint but grows with a wide joint on small tiles.
Why does the adhesive depend on the notched trowel?
The trowel sets how much adhesive is laid under each tile, so a bigger notch uses more adhesive per square metre. Use the figure on the adhesive's data sheet for the trowel you will use, and for the tile size.
How do I enter an L-shaped room?
Split it into two rectangles and type each on its own line. The calculator adds the two areas, so the tile count and the boxes cover the whole room.
Is the grout figure exact?
It is a calculation from the joint geometry and the density, not a measurement. It is usually close, but grout is sold in bags of a set size, so buy whole bags and keep the packaging coverage in mind.
Does the tool store what I enter?
No. The calculation runs in your browser and nothing you type is sent to us or stored.
Sources
Figures and text last checked on Tuesday, November 10, 2026.