How to calculate tiles
Divide the area you are covering by the area of one tile plus its grout joint. Grout lines look thin, but on small tiles they add up, so include them in the tile size.
Worked example: 10 × 8 ft bathroom floor, 12 × 24 in tile
The area is 80 sq ft. With a 1/8 in joint each tile covers 12.125 × 24.125 ÷ 144 = 2.03 sq ft. 80 ÷ 2.03 = 39.4 tiles, plus 10% waste = 44 tiles, or 6 boxes of 8.
Common tile sizes
| Tile size | Tiles per 100 sq ft (1/8 in joint, no waste) |
|---|---|
| 3 × 6 in subway | ≈ 752 |
| 12 × 12 in | ≈ 98 |
| 12 × 24 in | ≈ 49 |
| 24 × 24 in | ≈ 25 |
Grout joint guide
Rectified porcelain can use 1/16–1/8 in joints. Standard ceramic floor tile usually needs 1/8–3/16 in, and handmade or rustic tile 1/4 in or more. Follow the manufacturer's minimum.
Frequently asked questions
How much extra tile should I buy?
Add 10% for straight layouts and 15% for diagonal, herringbone, or rooms with many cuts. Large-format tile may need a little more because each broken piece is costly.
Do I include grout lines when calculating tile?
Yes. Add the joint width to the tile's width and length. It has a large effect on small tiles like mosaics and subway tile.
How many 12x24 tiles do I need for 100 square feet?
About 49 tiles before waste, or 55 with 10% waste.