How tile quantity is calculated
Space per tile = (tile length + joint) × (tile width + joint) ÷ 144 (sq ft)
Tiles = area ÷ space per tile
With waste = tiles × (1 + waste %), rounded up
Boxes = tiles ÷ tiles per box, rounded up
Including the grout joint matters little for large tiles but a lot for mosaics. The waste allowance covers cuts at walls and around fixtures plus breakage; diagonal and herringbone layouts need more. Your tile’s box label lists the pieces and square feet per box.
Worked example
A 6 × 10 ft bathroom floor (60 sq ft) in 12 × 24 in tiles with 1/8 in joints, 10% waste, 8 tiles per box:
| Space per tile (12.125 × 24.125 ÷ 144) | 2.031 sq ft |
|---|---|
| Tiles before waste | 29.5 |
| Tiles with 10% waste | 33 |
| Boxes of 8 | 5 |
Frequently asked questions
How much extra tile should I buy?
Most projects allow around 10% for cuts and breakage, more for diagonal patterns or natural stone. Keep leftovers for future repairs.
Does grout width change how many tiles I need?
Slightly. Wider joints mean each tile covers a little more area, so you need fewer tiles. The effect is noticeable with small tiles.