How this calculator works
Each tile covers its own size plus one grout joint, so the number of tiles is the area, plus your waste allowance, divided by the area of one tile with its joint. Boxes use the coverage printed on the box. Grout fills the joints: we work out the volume of joint per square metre from the tile size, joint width and thickness, convert it to kilograms at about 1.6 kg a litre, and add 20%. Adhesive depends on the notch of the trowel.
Worked example: a 3 × 2.5 m floor (7.5 m²) in 300 × 300 mm tiles with 3 mm joints and 10% waste: each tile with its joint covers 0.303 × 0.303 = 0.0918 m², so you need 8.25 ÷ 0.0918 = 89.9, which is 90 tiles (9 boxes at 1 m² a box). That takes about 37 kg of adhesive with a 10 mm trowel (two 20 kg bags) and 2.9 kg of grout (one 5 kg bag).
Tiles for common room sizes (300 × 300 mm tiles, 3 mm joints, 10% waste)
Boxes assume 1 m² a box, adhesive uses a 10 mm notch, and the bags are 20 kg adhesive and 5 kg grout.
| Area | Tiles | Boxes | Adhesive bags | Grout bags |
|---|---|---|---|---|
| 2 × 1.5 m (3.0 m²) | 36 | 4 | 1 | 1 |
| 2.5 × 2 m (5.0 m²) | 60 | 6 | 2 | 1 |
| 3 × 2.5 m (7.5 m²) | 90 | 9 | 2 | 1 |
| 4 × 3 m (12.0 m²) | 144 | 14 | 3 | 1 |
| 5 × 4 m (20.0 m²) | 240 | 22 | 5 | 2 |
| 6 × 5 m (30.0 m²) | 360 | 33 | 8 | 3 |
Tips before you buy
- Buy all the tiles from the same batch (check the batch or shade number on each box). Colour and size vary between batches, and tiles are hard to match later.
- Large-format tiles (over about 600 mm) and natural stone need more waste, a flatter floor, a bigger trowel and usually back-buttering.
- Use a flexible adhesive over underfloor heating and on timber floors, and wait for the screed to dry before you tile.
- Start from the centre of the room, or from the most visible line, and check the width of the last row before you fix the first, so that you do not end up with thin slivers at the edges.
- Keep a spare box. A tile that cracks later, or a repair after a leak, is hard to match.
Tools & materials for this project
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Frequently asked questions
How many tiles do I need for 10 square metres?
About 120 tiles of 300 × 300 mm with 3 mm joints and 10% waste, which is 11 m² of tile. Larger tiles need fewer, but more waste.
How much adhesive do I need per square metre?
Around 3 kg per m² for wall tiles with a 6 mm notch, about 4.5 kg for floor tiles with a 10 mm notch, and up to 6 kg for large tiles. A 20 kg bag therefore covers about 3 to 7 m².
How much grout do I need?
It depends on the tile size, joint width and thickness. 300 × 300 mm tiles with 3 mm joints use about 0.4 kg per m², but mosaics and wide joints need many times more.
How much extra tile should I buy?
10% for a straight layout, 15% for diagonal layouts or large tiles, and more for patterns or natural stone. Always buy a spare box.
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Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.