Tile Calculator
Tile is sold by the box and wasted by the layout. This counts pieces including the grout joint, applies a waste allowance that matches how you are setting them, and rounds up to whole boxes.
Tile quantity calculator
Waste by layout
| Layout | Allowance | Why it is higher |
|---|
Tiles per square foot by size
| Tile size | Tiles per sq ft | Coverage per tile |
|---|
Boxes, not tiles, is what you actually buy
Floor tile arrives in boxes that cover a fixed area — often 10 to 15 square feet depending on the size — and the box is the unit that goes on the receipt. A calculation that returns 65 tiles is useful, but 11 boxes is what you order, and the difference between the two is the spare you will want in two years when a chair leg chips a corner.
Keeping one spare box is not hoarding. Tile dye lots change, and a replacement box bought later will not match the floor you installed, even from the same product line.
How the count is calculated
Each tile occupies its nominal size plus half the grout joint on every side, so a 12 by 24 tile with a 1/8 inch joint actually covers 12.125 by 24.125 inches, which is 2.031 square feet. Divide the room area by that, add the waste allowance, and round up.
For a 120 square foot floor in 12 by 24 tile with a 10 percent allowance that is 120 divided by 2.031, which is 59.1 tiles, times 1.1 for 65 tiles, or 11 boxes of six. At $4.50 a square foot the material runs $594, and the boxes contain 66 tiles — one more than the count, which is exactly the spare you want.
Waste is a layout property, not a fudge factor
A straight lay in a rectangular room wastes about 10 percent, almost all of it at the perimeter where tiles are cut to fit. A diagonal lay cuts every edge tile on an angle, so waste climbs to 15 percent. Herringbone and chevron patterns waste 20 percent or more because every piece is cut from a different angle and offcuts rarely fit anywhere else.
Small rooms and rooms with many corners waste more than their area suggests. A 5 by 8 bathroom with a toilet alcove, a door and a vanity has more perimeter per square foot than a 20 by 20 kitchen, and every perimeter foot is a cut. When in doubt, round up a box rather than down.
What the floor area does not include
Wall tile is measured to the field, then the skirting, the niche returns, the window reveal and the shower curb are added separately — none of them appear in a length-by-width figure. A tub surround with two niches typically needs 6 to 10 extra square feet for the returns alone.
Also missing: the tile under the vanity that you pull up when the cabinet is replaced, the spare for a future repair, and the thinset coverage. Thinset is not tile, but it is a line item people forget, at roughly one 50 pound bag per 50 to 95 square feet depending on trowel size.
Choosing the grout joint
Rectified porcelain, which is cut to a precise size after firing, can take a 1/16 inch joint. Standard ceramic and natural stone are not dimensionally consistent, so they need 3/16 to 1/4 inch to absorb the variation; trying to set them tight produces lippage that no grout will hide. Larger joints also mean slightly more tiles per square foot are unnecessary — the joint is taking up area you do not need to cover.
Frequently asked questions
How many tiles do I need for a 10x12 room?
About 65 tiles of 12 by 24 with a 10 percent allowance, which is 11 boxes of six. A smaller tile means more pieces but the same area; a 12 by 12 tile would need roughly 130 pieces.
How many tiles are in a box?
It varies by size and manufacturer — six 12 by 24 tiles, ten 12 by 12s, or fifteen 6 by 6s are common. Check the box coverage in square feet, which is the number to compare across brands.
How much extra tile should I buy?
Ten percent for a straight lay, 15 for diagonal, 20 for herringbone. Always keep one unopened box after the job; dye lots change and a future repair will not match otherwise.
Do I need to account for grout joints?
Yes, but the effect is small. A 1/8 inch joint adds about 1.5 percent to the coverage of a 12 by 24 tile. It matters more for small tiles and wide joints, where the grout can take up 8 to 10 percent of the floor.
How do I calculate wall tile for a shower?
Measure each wall separately as width times height, add them, then subtract the shower valve opening and add back the niche returns and the curb. Do not use the floor area as a proxy.
How much thinset do I need?
Roughly one 50 pound bag per 50 to 95 square feet, depending on trowel notch size. A 1/4 inch notch covers about 95 square feet, a 1/2 inch notch about 50.
Can I use this for tile on a diagonal?
Set the waste allowance to 15 percent before calculating. The tile count per square foot does not change, only the number of cut pieces, and the allowance is what covers them.
Disclaimer: This calculator estimates tile and box counts from area and nominal tile size. Actual quantities depend on the layout, the size of the perimeter cuts, and the coverage printed on the box. Confirm the box coverage with your supplier.
Citing this page? FigureMill, “Tile Calculator” (last reviewed October 31, 2026). Tile and box count from floor area, nominal tile size and grout joint, with a layout-specific waste allowance. https://figuremill.com/materials/tile-calculator
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