Tile layout starts with square reference lines. If the first row is out of square, every grout line after it wanders, and the error is obvious at the far wall. Snap two perpendicular lines through the centre of the room and check them with 3-4-5 before setting a single tile. Then use this calculator to buy the right number of boxes.
Method
Each tile covers (tile length + joint) × (tile width + joint). Area ÷ coverage per tile gives the count; the waste factor covers cuts, breakage and spares. Divide by tiles per box and round up.
Waste factors
| Pattern | Waste |
|---|---|
| Straight lay, simple room | 10% |
| Brick / offset | 10–12% |
| Diagonal | 15% |
| Herringbone | 15–20% |
Keep at least one unopened box from the same lot for future repairs — dye lots change and a matching tile can be impossible to find later.
Watch: how it is done
Video by Davids Diy Reviews on YouTube. More in our video library.
Frequently asked questions
How do I square tile lines in a room?
Snap a centreline along the room, mark 3 ft from the centre point on that line and 4 ft on a perpendicular line, and adjust until the diagonal reads 5 ft. Use 6-8-10 for larger rooms.
Does grout width really change the count?
With small tiles, yes. A 1/4" joint on 4" tile adds about 12% coverage per tile, so you need noticeably fewer tiles.
Should I buy extra for a backsplash?
Yes. Backsplashes have many cuts around outlets and windows; 15% is a safer waste allowance.
Results are planning estimates. For structural work, confirm requirements with your local building authority and a qualified professional. See our disclaimer.