How to calculate how many tiles you need
Work out the area, divide by the area each tile covers including its grout joint, then add extra for cuts and breakage. Rounding up to whole boxes gives you a few spares, which are worth keeping for future repairs, since dye lots change.
Example: a 12 × 10 ft floor is 120 sq ft. A 12" × 24" tile with a 1/8" grout joint covers 12.125 × 24.125 ÷ 144 = 2.0314 sq ft, so the floor takes 59.07 tiles. Adding 10% brings it to 65 tiles, which is 9 boxes of 8.
How much extra tile to buy
| Layout | Extra |
|---|---|
| Straight lay, simple square room | 5% to 10% |
| Brick or offset pattern, most rooms | 10% |
| Diagonal, herringbone, many corners | 15% to 20% |
| Large-format tile (24" and up) | 15%, since each broken tile costs more |
For an L-shaped room, split it into rectangles and add the areas, or use the square footage calculator.
Frequently asked questions
How many tiles do I need for 100 square feet?
With 12" × 12" tiles and a 1/8" joint, about 98 tiles before waste, or 108 with 10% extra. Larger tiles need fewer: about 54 of a 12" × 24" tile with 10% extra.
Should I include grout lines?
Yes, for accuracy. Grout joints make each tile cover slightly more area, so you need a few percent fewer tiles than area ÷ tile size suggests, especially with small tiles.
How much thinset do I need?
A 50 lb bag covers roughly 80 to 95 sq ft with a 1/4" notch trowel for small tile, or 40 to 50 sq ft with the 1/2" notch used for large-format tile.
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