How to use the tile calculator
Enter the floor or wall size, the tile size and the grout joint you plan to use. Then choose the layout. The layout sets a typical waste allowance, which you can change. If you know how much one box covers, enter it to get a box count.
For an L-shaped room, split it into rectangles, add their areas and use the "I know the sq ft" option. Our guide to measuring odd-shaped rooms walks through it.
How the tile count is calculated
Each tile covers its own face plus half the grout joint on every side. That adds one full joint to each dimension:
- Coverage per tile (sq ft) = (tile width + joint) × (tile length + joint) ÷ 144
- Tiles before waste = area ÷ coverage per tile
- Tiles to buy = tiles before waste × (1 + waste %), rounded up
- Boxes = tiles ÷ tiles per box, or area with waste ÷ sq ft per box, rounded up
The grout joint matters more with small tiles. With 4 × 4 in tile, a 1/8 in joint adds about 6% to the area each tile covers. With 24 × 24 in tile it adds about 1%.
Waste by layout
| Layout | Typical waste | Why |
|---|---|---|
| Straight (grid) | 10% | Cuts only at the edges |
| Offset / brick | 10% | Offcuts from one row often start the next |
| Diagonal (45°) | 15% | Every edge tile is cut at an angle |
| Herringbone | 20% | Many angled cuts at every wall |
Tiles per 100 sq ft by tile size
Straight layout, 1/8 in grout joint, 10% waste:
| Tile size | One tile covers (sq ft) | Tiles per 100 sq ft |
|---|---|---|
| 4 × 4 in | 0.118 | 931 |
| 3 × 6 in | 0.133 | 828 |
| 6 × 6 in | 0.261 | 423 |
| 12 × 12 in | 1.021 | 108 |
| 12 × 24 in | 2.031 | 55 |
| 18 × 18 in | 2.281 | 49 |
| 24 × 24 in | 4.042 | 28 |
| 6 × 36 in | 1.537 | 72 |
| 8 × 48 in | 2.715 | 41 |
Worked example: a 10 × 12 ft bathroom floor
12 × 24 in porcelain, 1/8 in joints, laid in an offset pattern with a few extra cuts around the toilet and vanity, so 15% waste. The box says 15.5 sq ft.
- Area: 10 × 12 = 120 sq ft.
- Coverage per tile: (12.125 × 24.125) ÷ 144 = 2.031 sq ft.
- Tiles before waste: 120 ÷ 2.031 = 59.1.
- With 15% waste: 59.1 × 1.15, rounded up = 68 tiles.
- Boxes: 120 × 1.15 = 138 sq ft ÷ 15.5 = 9 boxes.
Mistakes that cost a second trip
- Buying exactly the area. Cuts, breakage and a few spares for future repairs all come out of the same boxes.
- Mixing lots. Boxes from different production runs can differ in shade. Check the lot number on each box.
- Ignoring the nominal size. A "12 × 24" tile can measure slightly less. Use the actual size on the box for tight layouts.
- Forgetting the walls. A tub surround or backsplash is a separate area. Calculate it on its own.
Questions people ask
How much extra tile should I buy?
10% for a straight or offset layout in a simple room, 15% for diagonal, and 20% for herringbone. Keep a few spare tiles after the job in case one cracks later.
Does grout width change how many tiles I need?
Slightly. A wider joint means each tile covers a bit more area, so you need fewer tiles. The effect is largest with small tiles.
Should I subtract the area under cabinets?
If the cabinets stay in place, yes. Tile under a dishwasher or range, though, so the appliance can come out at the same height.