Tile is sold by the box but laid one piece at a time, with a grout joint around each piece and plenty of cuts at the edges. This calculator takes the area you are covering, the tile size and the joint width, adds an allowance for cuts and breakage, and tells you how many tiles and boxes to buy — in US or metric units.
How to use the tile calculator
- Choose US (feet and inches) or Metric (meters, centimeters, millimeters).
- Enter the area as length × width or as a known area. For L-shaped rooms, total the pieces with the square footage calculator first.
- Enter the tile size and the grout joint width.
- Set the extra for cuts and breakage.
- Enter tiles per box and, optionally, the price per box.
Tile formulas
Each tile covers its own face plus one grout joint in each direction:
All lengths must be in the same unit, so the calculator converts room dimensions to inches (or centimeters) before dividing.
Worked example: a 12 × 10 ft floor
Area: 12 × 10 = 120 ft² = 17,280 in².
12 × 12 in tiles with 1/8 in joints: 12.125 × 12.125 = 147.02 in² per tile.
17,280 ÷ 147.02 = 117.5 tiles; with 10% extra, 129.3 → 130 tiles.
At 10 tiles per box, that is 13 boxes; at $32 a box, $416.
A straight grid on this floor uses 12 tiles across and 10 down — 120 positions including the cut pieces along two walls — which is why the 10% allowance is not excessive.
How much extra to buy
| Layout | Typical extra |
|---|---|
| Straight grid, simple room | 10% |
| Brick or offset pattern | 10–15% |
| Diagonal (45°) | 15% |
| Herringbone or chevron | 15–20% |
| Natural stone or fragile large-format tile | add 5% more |
Leftover tiles are worth keeping. Tile is made in production lots that vary slightly in color and size, so a matching replacement can be hard to find years later.
Choosing a grout joint
Joint width depends mostly on how uniform the tiles are. Rectified tiles, which are ground to precise dimensions, can be set with narrow joints, while handmade or pressed tiles need wider joints to hide size differences. The ANSI A108 installation standards call for a joint at least three times the tile’s actual size variation and never narrower than 1/16 inch. Many floor installations use 1/8 to 3/16 inch; large-format floor tiles often use 3/16 inch, and wall tile commonly 1/16 to 1/8 inch.
Tiles per 10 square feet
| Tile size | Tiles per 10 ft² (face area only) |
|---|---|
| 3 × 6 in subway | 80 |
| 6 × 24 in plank | 10 |
| 12 × 12 in | 10 |
| 12 × 24 in | 5 |
| 18 × 18 in | 4.4 |
| 24 × 24 in | 2.5 |
These counts ignore grout and waste; the calculator includes both. Remember to budget for thinset mortar, grout, spacers and, for floors, an underlayment or backer board.
Frequently asked questions
How many 12 × 12 tiles do I need for 100 square feet?
With 1/8-inch grout joints each tile occupies about 147 square inches, so 100 ft² (14,400 in²) needs about 98 tiles. Adding 10% for cuts and breakage brings the order to 108 tiles.
How much extra tile should I buy?
Plan on about 10% for a straight layout in a simple room, 15% for diagonal layouts or rooms with many corners, and 15–20% for herringbone or other complex patterns. Natural stone and large-format tiles that break easily may justify a little more.
Does the grout joint change how many tiles I need?
Slightly. Each joint adds to the space a tile covers, so wider joints mean fewer tiles. With 12-inch tiles, going from 1/16-inch to 1/4-inch joints reduces the count by about 3%. With small mosaic or subway tiles, the effect is larger.
How do I calculate tile for a backsplash or wall?
Measure each wall section as a rectangle, subtract large openings such as windows, and add the areas. Small cutouts for outlets do not need to be subtracted. Enter the total as a known area.
How many boxes of tile should I order?
Divide the tile count, including the waste allowance, by the number of tiles in a box and round up. The box label usually also lists square feet per box, which is a handy cross-check.