How to use this calculator
- Measure the length and width of the floor or wall, or enter the area if you already know it.
- Subtract anything that won't be tiled, such as a shower tray or fitted units.
- Enter the tile size and the joint width you plan to use.
- Choose your layout. The spare percentage fills in automatically; change it if your tiler recommends another figure.
- Add tiles per box to see how many boxes to buy.
The formula
Area to tile = length × width − area not tiled
Space one tile takes = (tile length + joint) × (tile width + joint)
Tiles = area to tile ÷ space one tile takes
Tiles to buy = tiles × (1 + spare %), rounded up
Boxes = tiles to buy ÷ tiles per box, rounded up
Each tile takes up its own size plus half a joint on every side, which is why the joint is added to the tile size. Wide joints on small tiles make a real difference.
The spare covers cut tiles along the edges and the odd breakage. Straight and brick layouts usually need about 10 %; diagonal and herringbone layouts create more cuts, so 15 % is common. Small rooms with many corners may need more.
Worked example
A 3 m × 2 m floor is 6 m².
With 300 mm × 300 mm tiles and 3 mm joints you need 65.4 tiles before spares.
Adding 10% for cuts gives 72 tiles, which is 7 boxes of 11.
Tips before you buy
- Check that every box has the same batch or shade code — tiles from different batches can look slightly different.
- Keep at least one spare box after the job so you can replace a cracked tile later.
- Large-format tiles (60 cm and above) are heavy and need a flat floor; ask about levelling before you buy.
- Want to see the layout first? Try the tile visualizer to count whole and cut tiles for your exact room.
Frequently asked questions
›How much extra tile should I buy?
About 10 % for straight or brick layouts and about 15 % for diagonal or herringbone. Add more for small rooms with lots of corners, or if the tiles are fragile.
›Does the grout joint change how many tiles I need?
Yes. Each tile covers its own size plus the joint, so wider joints mean slightly fewer tiles. With small mosaic tiles the difference is significant.
›How do I measure an L-shaped room?
Split it into rectangles, work out each area, and add them up. Our square footage calculator does this for you; enter the total here using the "Enter the area" option.
›Should I round up to whole boxes?
Yes. Tiles are usually sold by the box, so the calculator always rounds up. Leftover tiles are useful for future repairs.
Sources
- Formula: standard tile coverage method (tile + joint footprint). Waste allowances: common trade guidance.
Formulas last reviewed: September 29, 2026. How we check our formulas