How to Calculate Tile and Flooring Quantity
Room area, tiles per square foot, layout overage and rounding up to full boxes
How to calculate tile quantity: the short version
Measure the area to be covered, add an overage allowance for your layout, then divide by the coverage of one box and round up. The overage is the part people most often get wrong, because it depends on the layout, the tile size and the shape of the room rather than on a single fixed percentage.
- Measure the floor or wall area, splitting irregular rooms into rectangles.
- Leave out large fixed areas that won't be tiled, such as a kitchen island footprint.
- Choose an overage for the layout and multiply the area by it.
- Divide by the coverage per box and round up to whole boxes.
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.
The Floor Area Calculator adds up the sections of an L-shaped or irregular room.
How many tiles per square foot
If you count tiles rather than boxes, divide the area by the area of one tile. The table gives the exact counts for common sizes, before any overage or grout-joint allowance.
| Tile size (in) | Area of one tile | Tiles per ft² | Tiles per 100 ft² |
|---|---|---|---|
| 3 × 6 | 0.125 ft² | 8.00 | 800 |
| 6 × 6 | 0.25 ft² | 4.00 | 400 |
| 12 × 12 | 1.00 ft² | 1.00 | 100 |
| 12 × 24 | 2.00 ft² | 0.50 | 50 |
| 18 × 18 | 2.25 ft² | 0.44 | 44.4 |
| 24 × 24 | 4.00 ft² | 0.25 | 25 |
How much overage to add for each layout
A straight, grid-aligned layout needs the least extra material, because only the perimeter tiles are cut. A diagonal (45°) layout needs more, because every edge tile takes an angled cut and more of each tile is lost. Herringbone and other complex patterns can need more again, depending on the pattern and tile proportions.
There is no single published standard for tile overage, and recommendations vary widely. The presets in the Tile Waste Calculator reflect common trade practice. Some tile sellers recommend considerably more: Artistic Tile, for example, advises 20% for a straight lay, 25–30% for a diagonal layout and at least 30% for tiles 18 × 36 in and larger.
| Layout | BuildNumerics Tile Waste Calculator preset |
|---|---|
| Straight / grid | 10% |
| Diagonal | 15% |
| Herringbone or pattern | 20% |
| Large-format tile or a very cut-up room | 25% |
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.
The Tile Calculator gives tile and box counts from the tile size, and the Flooring Calculator does the same for plank flooring. Grout and thinset are calculated separately — see Tile, Grout and Thinset.
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
Same room laid diagonally with the 15% preset: 120 × 1.15 = 138 ft² → 138 ÷ 15 = 9.2 → 10 boxes
FAQ
- How much extra tile should I buy?
- It depends on the layout, tile size and room shape. The BuildNumerics Tile Waste Calculator presets are 10% for a straight grid, 15% for diagonal, 20% for herringbone or patterns and 25% for large-format tile or a very cut-up room. Some tile sellers recommend more, so check your supplier's guidance.
- How many tiles do I need for 100 square feet?
- Before overage, 100 tiles of 12 × 12 in, 50 tiles of 12 × 24 in or 25 tiles of 24 × 24 in. Divide 144 by the tile's length times width in inches to get tiles per square foot, then add your overage.
- 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.
Related Calculators
From the Blog
Sources
Artistic Tile, How to Measure
Seller guidance on overage by layout, tile size and project type.
Artistic Tile, How to Measure — reference