The method

How this calculator works

Count the tiles in each direction

Tiles are laid in rows, so the calculator works out how many fit across the width and down the length, rounding each up to a whole tile. Multiplying the two gives the number of tiles needed before waste.

With a grout gap, a row of n tiles has n − 1 gaps, so it covers n × tile + (n − 1) × gap. The calculator finds the smallest n that spans the area. For a 30 cm tile and a 3 mm gap, that is the same as dividing the area plus one gap by the tile plus one gap.

Allow for cuts and spares

Edge tiles usually need cutting, and some break. A commonly used allowance is about 10% for a straight layout and 15% for diagonal or patterned layouts. The calculator adds your allowance and rounds up to whole tiles.

Keep the leftovers. Tiles from a later batch can differ slightly in shade and size, so a few spares from the same batch make future repairs far easier.

Check the tile and the layout before ordering

Use the actual tile size on the box, which can differ from the name. A '30 × 30 cm' tile may be a few millimetres smaller. Dry-lay a row on the floor with spacers to check where the cuts will fall.

If the last tile in a row would be a thin sliver, consider starting from the centre of the room or shifting the layout so the cuts at both ends are equal and larger.

Worked example

Example: a 3 m × 2.5 m floor with 30 cm tiles

  1. Along the 300 cm length: (3000 + 3) ÷ (300 + 3) = 9.9, which rounds up to 10 tiles.
  2. Along the 250 cm width: (2500 + 3) ÷ (300 + 3) = 8.3, which rounds up to 9 tiles.
  3. 10 × 9 = 90 tiles. Add 10% waste: 99 tiles.
  4. With 10 tiles in a box, 99 tiles means 10 boxes (100 tiles).

Practical answer: Buy 99 tiles, or 10 boxes if the boxes hold 10 tiles each. That leaves one spare tile, so consider an extra box if the layout is diagonal or the room has many corners.

Before you buy

Common measuring mistakes

  • Dividing the floor area by the area of one tile, which ignores the cut tiles at the edges.
  • Forgetting the waste allowance, then being unable to match the batch for the last few tiles.
  • Using the nominal tile size instead of the measured size on the box.
  • Leaving out the grout gap, which adds up over a long row.
  • Tiling a wall as one rectangle without taking out windows, doors and fixed units.