How many tiles do I need?
Area covered by one tile = (tile length + joint) × (tile width + joint)
Tiles = area ÷ area per tile × (1 + waste %), rounded up
The grout joint matters more than people expect with small tiles: each tile effectively covers its own size plus one joint in each direction. For large tiles the joint makes little difference. Inches are converted to square feet by dividing by 144 (12 × 12).
Worked example: bathroom floor
An 8 × 5 ft bathroom floor is 40 sq ft. With 12 × 12 in tiles and a 1/8 in (0.125 in) grout joint:
- Each tile covers 12.125 × 12.125 = 147.02 sq in = 1.021 sq ft.
- Tiles without waste: 40 ÷ 1.021 = 39.2.
- With 10% waste: 39.2 × 1.10 = 43.1, so buy 44 tiles, which is 5 boxes of 10.
Worked example: subway tile backsplash
A backsplash 10 ft long and 18 in (1.5 ft) high is 15 sq ft. Subway tiles of 3 × 6 in with a 1/16 in (0.0625 in) joint each cover 3.0625 × 6.0625 = 18.57 sq in, or 0.129 sq ft. That is 15 ÷ 0.129 = 116.3 tiles, and with 10% waste 128 tiles. Subtract the area of outlets and windows if they are large.
Tiles per square foot for common sizes
| Tile size | Tiles per sq ft (no joint) | Sq ft per tile |
|---|---|---|
| 3 × 6 in (subway) | 8 | 0.125 |
| 4 × 4 in | 9 | 0.111 |
| 6 × 6 in | 4 | 0.25 |
| 12 × 12 in | 1 | 1 |
| 12 × 24 in | 0.5 | 2 |
| 24 × 24 in | 0.25 | 4 |
How much waste to allow
A 10% allowance covers cuts at the walls and the odd broken tile in a normal room. Use 15% for a diagonal layout or large-format tiles (where each wasted cut is a big piece), and around 20% for herringbone. For showers and small rooms with many cuts around niches and fixtures, err on the high side. Keep a few spare tiles from the same batch for future repairs, because colour can vary between production lots.
Showers and walls
For a shower, work out each wall separately (width × tiled height) and add them, then subtract the doorway or glass panel. A shower with a 5 ft back wall and two 3 ft side walls, tiled 7 ft high, has (5 + 3 + 3) × 7 = 77 sq ft of wall. Calculate the shower floor separately if it uses a different, smaller tile.
Grout and adhesive
Grout and thinset coverage depends on the tile size, thickness, joint width and trowel notch, so use the coverage chart on the bag or the manufacturer's online calculator. As a general rule, narrow joints with large tiles use very little grout, and small mosaics use much more.
Step by step: planning a tile job
- Measure each surface to tile separately: floor, each wall, the backsplash.
- Subtract large openings such as windows, doors and a bathtub front.
- Measure the actual tile size from a sample, not the name on the box.
- Pick the grout joint width the tile manufacturer recommends.
- Choose the waste allowance for your layout and round the boxes up.
Common mistakes
- Confusing nominal and actual tile size. Some tiles sold as 12 × 12 measure 11.8 in; use the actual size from the box.
- Ignoring the joint with small tiles, which overestimates how many you need.
- Not buying enough from one lot. A second order later may not match in colour.
Frequently asked questions
How many 12×12 tiles do I need for 100 square feet?
Without joints, 100 tiles. With a 1/8 in joint each tile covers about 1.021 sq ft, so about 98 tiles, and with 10% waste about 108 tiles.
How do I calculate tiles per square foot?
Divide 144 by the tile area in square inches. A 6 × 6 in tile is 36 sq in, so 144 ÷ 36 = 4 tiles per square foot.
How much extra tile should I buy?
About 10% for a standard layout, 15% for diagonal or large-format tile and 20% for herringbone. Keep a few spare tiles for repairs.
Does grout width change the number of tiles?
Slightly. Each tile covers its size plus one joint each way, so wider joints mean fewer tiles. The effect is large for mosaics and small for big tiles.
How many tiles are in a square metre?
Divide 1 by the area of one tile plus its joint in square metres. A 30 × 30 cm tile with a 3 mm joint covers 0.303 × 0.303 = 0.0918 m², so about 10.9 tiles per square metre before waste.
Sources
- Tile Council of North America (TCNA), Handbook for Ceramic, Glass, and Stone Tile Installation: grout joint and layout guidance.
- Tile manufacturers' installation guides (typical 10% overage; more for diagonal and patterned layouts).
Last reviewed 20 October 2026. Results are estimates; see our disclaimer.