How to Calculate Tile and Flooring Quantity
Room area, layout waste, and why diagonal patterns need more material
Start with room area
Measure the room's length and width and multiply for a rectangular room, or break an irregular room into rectangular sections and add the areas together. Measure to the walls, not to existing baseboards or trim you plan to remove.
Layout pattern changes the waste allowance
A straight, grid-aligned layout typically needs the least extra material — often a 10% allowance covers edge cuts. A diagonal (45°) layout usually needs more, often 15-20%, because every edge tile requires an angled cut and more of the tile is wasted. Herringbone and other complex patterns can need even more, depending on the specific pattern and tile proportions.
Tile size and room shape both matter
Larger tiles in a small or irregularly-shaped room waste proportionally more material, since each cut tile loses a bigger piece relative to the tile's total size. A room with many corners, alcoves, or fixtures (like a bathroom around a toilet and vanity) also needs a higher allowance than a simple rectangular room.
Boxes, not individual tiles
Tile and plank flooring are sold by the box, covering a fixed area per box (printed on the packaging). Once you have your waste-adjusted area, divide by the coverage-per-box to get the number of boxes, and round up — a partial box still needs to be purchased in full.
Worked Example
A 120 ft² room, straight layout, 10% waste, tile sold in boxes covering 15 ft² each.
Waste-adjusted area: 120 × 1.10 = 132 ft²
Boxes needed: 132 ÷ 15 = 8.8 → round up to 9 boxes
FAQ
- Should I buy extra tile beyond what the calculation says, for future repairs?
- Many installers keep one extra box as 'attic stock' for future repairs, since tile lines are frequently discontinued. This is a separate decision from the waste allowance, which only covers cutting loss during the original installation.
- Do grout and thinset use the same waste allowance as the tile itself?
- No — grout and thinset quantities depend on tile size, grout-line width, and trowel-notch size, not on the tile's cut waste. Calculate them separately.