How this calculator works
Enter the floor's length and width, the size of a single tile, and a waste allowance percentage, in either centimeters or inches. The calculator divides floor area by tile area to get a raw tile count, adds the waste percentage to cover cuts and breakage, and rounds up to a whole tile — then, if you enter how many tiles come in a box, rounds that up to a whole box too.
A waste allowance of 10% is a common starting point for a simple rectangular room laid in a straightforward grid pattern; more complex layouts (diagonal patterns, herringbone, rooms with lots of corners or fixtures to cut around) typically need 15% or more. This calculator does not model grout lines or tile spacing directly — the waste percentage is assumed to absorb both the cutting waste and the small area grout lines take up.
The formula
Floor area = floor length × floor width; tile area = tile length × tile widthTiles needed = ceiling( (floor area ÷ tile area) × (1 + waste % ÷ 100) )Boxes needed = ceiling(tiles needed ÷ tiles per box), if tiles per box is providedAll areas are computed in the tile and floor's native unit (cm² or in²) before the waste multiplier and rounding, then displayed in the more familiar m² or ft².
Worked example: a 400 cm × 300 cm floor with 30 cm tiles
- Floor area: 400 × 300 = 120,000 cm² (12 m²). Tile area: 30 × 30 = 900 cm².
- Raw tile count: 120,000 ÷ 900 ≈ 133.3 tiles.
- With 10% waste: 133.3 × 1.10 ≈ 146.7, rounded up to 147 tiles.
- At 10 tiles per box: 147 ÷ 10 = 14.7, rounded up to 15 boxes.
Frequently asked questions
Why does the calculator round up instead of giving the exact decimal?
You cannot buy a fraction of a tile or a fraction of a box. Rounding the tile count and the box count up separately (rather than rounding only once at the end) guarantees you have enough tiles to finish the job, even if it means a few extra full tiles left over.
How much waste allowance should I use?
10% is a reasonable default for a simple rectangular room in a straight grid layout. Increase it to 15% or 20% for diagonal or herringbone patterns, rooms with many corners, alcoves or fixtures to cut around, or if you are a first-time tiler expecting more breakage.
Does this account for grout lines between tiles?
Not directly. Grout lines take up a small amount of floor area that would otherwise be tile, but the effect is minor for typical grout widths (a few millimeters) and is generally covered by the same waste allowance used for cutting losses.
What if my tiles aren't square?
Enter the tile's actual length and width — the formula multiplies them together for area regardless of whether the tile is square or rectangular, so non-square tiles (like common plank-style tiles) work the same way.
Should I buy exactly the calculated number of boxes?
Buying exactly the rounded-up amount leaves little room for mistakes discovered mid-project. Many installers buy one extra box beyond the calculated amount, especially for patterned tile or a floor that may need future repairs matched to the same batch.