How to use the tile calculator
- Enter the size of the floor or wall area, or its total area. For several walls, add up their areas first.
- Enter the tile size and the grout joint width. In US mode tile sizes are in inches; in UK mode they are in millimetres.
- Choose a waste allowance — 10% for straight layouts, more for diagonal or herringbone patterns.
- Add the number of tiles per box to see how many boxes to buy.
The tile formula
Tile footprint = (tile length + joint) × (tile width + joint) Tiles = area ÷ tile footprint × (1 + waste % ÷ 100)
Including the joint matters more than you might think: on small tiles, the grout lines take up a noticeable share of the surface.
Worked example (US)
A 10 × 10 ft bathroom floor (100 ft²) with 12 × 12 inch tiles and 1/8 inch joints: each tile covers 12.125 × 12.125 = 147 in², or 1.02 ft². 100 ÷ 1.02 = 98 tiles, or 108 tiles with 10% extra.
Worked example (UK)
A 3 × 2.5 m kitchen floor (7.5 m²) with 600 × 300 mm tiles and 3 mm joints: each tile covers 0.603 × 0.303 = 0.183 m². 7.5 ÷ 0.183 = 42 tiles, or 46 tiles with 10% extra.
Waste allowance by layout
| Layout | Typical waste |
|---|---|
| Straight grid | 10% |
| Brick bond / offset | 10–15% |
| Diagonal | 15% |
| Herringbone | 15–20% |
Tiling tips
- Buy from one batch. Check the shade and batch codes on every box — they can vary between production runs.
- Keep a few spares for future repairs; discontinued tiles are very hard to match.
- Plan your layout from the centre of the room so cut tiles at each edge are equal and not too thin.
- Tiling over new walls? The drywall & plasterboard calculator covers the boards (use moisture-resistant or cement board in wet areas).
Frequently asked questions
How many tiles do I need per square metre?
It depends on tile size. With 3 mm joints you need about 2.75 tiles per m² for 600 × 600 mm tiles, 5.5 for 600 × 300 mm and 11 for 300 × 300 mm — before adding waste.
How many 12 × 12 tiles do I need for 100 square feet?
About 98 tiles with 1/8 inch grout joints, or 108 tiles once you add 10% for cuts and breakages.
How much extra tile should I buy?
Add 10% for straight layouts, 15% for diagonal or offset patterns, and 15–20% for herringbone or rooms with many cuts. Large-format tiles break more expensively, so lean towards the higher figure.
Do I subtract the bath or shower tray area?
Yes. Measure only the surface you will actually tile. For walls, measure each wall separately and subtract windows, doors and fitted units, then add the walls together.
What grout joint size should I use?
Rectified (precisely cut) tiles can use joints as narrow as 1/16 inch (2 mm). Most wall tiles use 1/16–1/8 inch (2–3 mm) and floor tiles 1/8–1/4 inch (3–5 mm). Check the tile manufacturer’s recommendation.