Tile Calculator

About the Tile Calculator

Tiling a floor or wall means buying tiles by the box, and running out halfway through is more than an inconvenience. The next delivery may come from a different production batch, a shade lighter or darker, and the difference can show clearly once the tiles are laid side by side. Getting the count right the first time matters more with tiles than with most materials.

The count itself comes from three things: the area to be tiled, the space each tile takes up — including the grout joint around it — and a waste allowance for cutting. The waste allowance is the one people most often get wrong, because it depends far more on the layout pattern than on the tile.

This tile calculator divides the area by the tile-plus-joint size, adds waste according to the layout you choose, and, if you give it the number of tiles per box, tells you how many boxes to buy.

How to Use the Tile Calculator

Choose metric (square metres and millimetres) or imperial (square feet and inches).

Enter the area to tile. For a floor, that is length times width; for walls, the height times the length of each wall, less windows and doors.

Enter the tile width and length and the grout joint width. Joints of 2 to 3 mm are typical on walls, 3 to 5 mm on floors.

Choose the layout: straight, brick bond, diagonal or herringbone. The waste allowance defaults to suit it, and you can override it.

Optionally, enter the tiles per box to get a box count.

How the Tiles Are Worked Out

  tiles per m²  =  1 ÷ ((tile width + joint) × (tile length + joint))
  tiles         =  area × tiles per m² × (1 + waste %), rounded up
  boxes         =  tiles ÷ tiles per box, rounded up

Step-by-Step Example

A 10 m² floor, 300 × 300 mm tiles, 3 mm joints, straight lay, 11 tiles per box.

  Tile with joint:  0.303 × 0.303 m        →  10.89 tiles per m²
  For the area:     10 × 10.89             =  109 tiles
  With 10% waste:   109 × 1.10             =  120 tiles
  Boxes:            120 ÷ 11               =  10.9  →  11 boxes

Why the Joint Is Included

Each tile covers not only its own face but a grout joint along one side and one end. With 3 mm joints on 300 mm tiles, that is 1% of each dimension and about 2% of the area. Ignoring it gives 11.1 tiles per square metre instead of 10.9 — a couple of extra tiles in every hundred. It is not large, but there is no reason to get it wrong, and on small tiles with wide joints the difference is much bigger.

Waste Depends on the Layout

The waste allowance covers tiles that are cut and whose offcuts cannot be used elsewhere, plus the odd breakage. How much is cut depends on the layout.

Straight or grid — tiles are cut only along the edges of the room, so about 10% is usually enough.

Brick bond — offset rows, like bricks, with cut tiles at alternate row ends: also about 10%.

Diagonal — the grid is turned 45°, so every tile along every edge is cut at an angle, and many offcuts are unusable: about 15%.

Herringbone — rectangular tiles in a zigzag; every edge tile is cut on an angle and the pattern needs precise alignment: about 20%.

Rooms with lots of corners, pipes, recesses or a kitchen island need more. Large-format tiles also waste more, because every offcut is large and a single broken tile is a big share of a box.

Tile Sizes and Counts

The number of tiles per square metre falls quickly as tiles get bigger. With 3 mm joints, 100 mm tiles need about 94 per square metre, 300 mm tiles about 11, and 600 mm tiles fewer than 3. Larger tiles mean fewer joints and faster laying, but they need a flatter surface underneath and more care to avoid lippage — one tile edge sitting proud of the next.

Planning the Layout

A few minutes planning before the first tile goes down saves tiles and gives a better-looking result.

Find the centre. Snap chalk lines through the middle of the room in both directions and dry-lay a row of tiles along each. Shifting the start point so the cut tiles at opposite walls are equal, and at least half a tile wide, avoids thin slivers at one side.

Start where it shows. In a bathroom, full tiles along the bath or the doorway look better than cut ones; put the cuts where furniture or fittings hide them.

Check the walls. Few walls are straight or square. Measure the room's diagonals; if they differ, the cuts along one wall will taper, which is another reason to allow the full waste.

Mind the adhesive. Large tiles need a notched trowel with deeper notches and sometimes back-buttering, which uses more adhesive per square metre.

Understanding Your Result

Tiles needed is the total including waste.

Boxes gives the box count if you entered the tiles per box.

Tiles per area shows the rate including joints.

Waste shows the tiles for the area and the allowance on top.

Worth knowing covers batches and patterned layouts.

When Should You Use This Calculator?

Before buying floor or wall tiles, to order enough from one batch.

When choosing between tile sizes or layouts, to compare the counts.

For a bathroom or kitchen, working each wall and the floor separately.

Checking a tiler's estimate.

Common Mistakes

Forgetting the waste allowance. Cuts use more than you think.

Using straight-lay waste for a diagonal or herringbone layout.

Mixing batches. Check the shade code on every box.

Not keeping spares. A cracked tile years later needs an exact match.

Subtracting small fixtures. Tiling around them uses the offcuts anyway.