Divide the area by the footprint of one tile including a grout line — (tile length + grout) × (tile width + grout) — then add 10–15% for cuts and round up to whole boxes. A 12 m² area with 30 × 30 cm tiles needs about 131 tiles before the allowance, or about 144 tiles once waste is included.
Tile sizes and grout widths
| Tile | Metric | Imperial | Typical grout width |
|---|---|---|---|
| Mosaic / small | 5 × 5 cm | 2 × 2 in | 2–3 mm (1/16–1/8 in) |
| Subway | 7.5 × 15 cm | 3 × 6 in | 2–3 mm (1/16–1/8 in) |
| Standard square | 30 × 30 cm | 12 × 12 in | 3 mm (1/8 in) |
| Large rectangle | 30 × 60 cm | 12 × 24 in | 3–5 mm (1/8–3/16 in) |
| Large format | 600 × 600 mm | 24 × 24 in | 3–5 mm (1/8–3/16 in) |
| Large format | 800 × 800 mm | 31.5 × 31.5 in | 3–5 mm (1/8–3/16 in) |
| Extra large | 1000 × 1000 mm | 39.4 × 39.4 in | 3–5 mm (1/8–3/16 in) |
| Porcelain slab | 1200 × 2400 mm | 47.2 × 94.5 in | Project-specific |
Large-slab planning: 1200 × 2400 mm slabs need specialist handling, cutting equipment, and a layout plan. Openings, corners, grain direction, and breakage can make a simple area-based 10% allowance insufficient, so confirm whole-slab quantities with the installer or supplier.
Understand the formula
The tile count is not simply area divided by the tile's face area, because grout pushes every tile apart. For this grid-layout approximation, include one shared grout line in each direction of the tile pitch before dividing.
Tiles = area ÷ ((tile length + grout) × (tile width + grout))Purchase tiles = ceil(Tiles × (1 + waste%))Boxes = ceil(Purchase tiles ÷ tiles per box)Why waste matters
| Condition | Likely effect | Planning response |
|---|---|---|
| Straight grid layout | Least waste | 10% allowance is usually enough |
| Diagonal or herringbone | More cuts and offcuts | Plan 15% or more |
| Non-rectangular room | Many edge cuts | Add extra allowance |
| Large format tiles | Bigger offcuts per partial tile | Add extra allowance |
Worked examples
12 × 12 ft floor
A 144 sq ft floor with 12 × 12 in tiles and 1/8 in grout has a base estimate of about 141.1 tiles, rounded up to 142 whole tiles. With 10% waste that is 156 tiles, or 16 boxes of 10: 14 tiles are the cutting-waste allowance and 4 more come from rounding to full boxes.
3 × 4 m floor
A 12 m² floor with 30 × 30 cm tiles and 3 mm grout needs about 131 tiles exactly. With 10% waste that is 144 tiles, or 15 boxes of 10 with 6 spare tiles.
Backsplash
A 2 m² backsplash with 7.5 × 15 cm subway tiles and 3 mm grout needs about 160 tiles. Because tiles-per-box varies, always round the final count up to the box size printed on the package.
Frequently asked questions
Should I buy extra tiles?
Yes — buy whole boxes and keep the spare. Shade can vary between production runs, so keeping extras from the same batch is essential for later repairs.
Does grout width really matter?
Yes. A 12 in tile with a 1/8 in grout line occupies 12.125 in, and that difference compounds across a whole wall.
Can I use the same calculation for walls and floors?
Yes, the math is identical. Enter the actual tile dimensions from the box label.
Sources and methodology
- Tile counts follow the standard grid-layout approximation used by most material estimators: area divided by the tile-plus-grout footprint, plus a waste allowance, rounded up to full boxes.
Use the tile calculator to run these numbers for your own measurements.
