Tile Calculator
Tiles are bought by the box, so the number you need is the number you must round up to. This calculator works out the count and adds a wastage allowance.
Formula
Tiles needed = area to cover ÷ area of one tile, plus wastage
- Add 10% for a straight lay, 15% for diagonal or a room with many cuts
12 m² with 300 × 300 mm tiles: 12 ÷ 0.09 = 134 tiles, 147 with 10% waste
The Calculation
Tiles needed = Area to cover ÷ Area of one tile
A 3 m × 2.5 m floor is 7.5 m². With 600 × 300 mm tiles (0.18 m² each): 7.5 ÷ 0.18 = 41.7 tiles, so 46 tiles once 10% wastage is added.
Convert tile dimensions to metres before dividing — mixing millimetres with metres is the error that produces answers a thousand times out.
How Much Wastage
- 10% for a simple square or rectangular room laid straight
- 15% for diagonal layouts, which generate far more cuts
- 15–20% for herringbone and other patterned work
- Add more for rooms with alcoves, pipework or many corners
Buy it all in one go and check the batch numbers match: tile colour varies noticeably between production runs, and a mid-job top-up rarely blends invisibly.
Beyond the Tiles
Adhesive and grout are usually sold by coverage per square metre, and both depend on tile size and trowel notch — large-format tiles need more adhesive, small mosaics need far more grout.
Keep a few spare tiles after the job. Cracking one in five years is common, and matching a discontinued range is close to impossible.
Quick Reference
| Tile size | Per m² | For 12 m² + 10% |
|---|---|---|
| 100 × 100 mm | 100 | 1,320 |
| 150 × 150 mm | 44.4 | 587 |
| 300 × 300 mm | 11.1 | 147 |
| 600 × 300 mm | 5.6 | 74 |
| 600 × 600 mm | 2.8 | 37 |
Frequently Asked Questions
- How many tiles do I need?
- Divide the area to cover by the area of one tile, then add 10 per cent for wastage and round up to whole boxes.
- How much extra should I order?
- 10 per cent for straight layouts, 15 per cent for diagonals, and up to 20 per cent for herringbone or rooms with lots of cuts.
- Do I need to worry about batch numbers?
- Yes. Tile colour varies between production batches, so buy the whole job at once and check the batch codes match.
- How much adhesive will I need?
- It depends on tile size and trowel notch. Check the coverage per square metre on the bag; large-format tiles need noticeably more.