Tile Calculator

How to work out how many tiles you need

Tiles are laid with a gap between them, so each tile takes up a little more floor than its own face. The calculator allows for that gap, then adds a margin for cut tiles and breakage and rounds up to whole tiles and boxes.

1. Measure the floor or wall. For an L-shaped room or a floor with a separate hallway, add each rectangle as its own area.
2. Enter the tile size and the grout joint width. Nominal sizes on the box (such as 12 × 12 in or 30 × 30 cm) are fine; for an exact figure, measure a tile.
3. Choose a waste allowance. Around 10% is common practice for a straight layout; diagonal, herringbone and other patterned layouts produce more offcuts and usually need more. The tile maker or your installer may recommend a figure.
4. Add the tiles per box and a price if you want the number of boxes and the cost.

Tile formula with grout joints

A

area to tile (length × width of each area, added up)

L, W

tile length and width

j

grout joint width

⌈ ⌉

round up to a whole tile

Why add one joint to each side? In a grid, every tile is surrounded by joints that it shares with its neighbors: half a joint on each edge. Half a joint on the left plus half on the right adds one full joint to the width, and the same happens top to bottom. So a 12 in tile with 1/8 in joints repeats every 12.125 in, and one tile with its joint takes up (12.125 ÷ 12)² = 1.0209 ft² rather than 1 ft².

Boxes are the tile count divided by the tiles per box, rounded up. Areas convert with the exact factor 1 ft² = 0.09290304 m².

Worked example

A 12 × 10 ft kitchen floor, 12 × 12 in tiles, 1/8 in joints and 10% waste:

1. Area: 12 × 10 = 120 ft²
2. One tile with its joint: (12 + 0.125) in × (12 + 0.125) in = 1.0209 ft²
3. Tiles to cover the floor: 120 ÷ 1.0209 = 117.54
4. With 10% waste: 117.54 × 1.10 = 129.29, so 130 tiles
5. In boxes of 15 at $30 a box: 130 ÷ 15 = 8.67, so 9 boxes (135 tiles) for $270

Ignoring the joint would give 120 × 1.10 = 132 tiles, two more than needed. The difference grows with smaller tiles and wider joints: with 4 × 4 in tiles and 1/4 in joints, the joint takes up about 11% of the floor (1 − 4² ÷ 4.25²).

In metric, a 4 × 3 m floor (12 m²) with 30 × 30 cm tiles and 3 mm joints: each tile takes 0.303 × 0.303 = 0.091809 m², so 12 ÷ 0.091809 = 130.71 tiles, and with 10% waste 143.78, or 144 tiles.

Waste, layout and spare tiles

• Layout drives waste. A straight grid in a plain rectangular room wastes least. Diagonal layouts cut every edge tile at an angle, and small rooms, many corners, pipes and cabinets all add cuts.
• Large tiles waste more per cut, because an offcut is often too small to reuse elsewhere.
• Keep a few spares. A later repair is easier with tiles from the same batch; the same product from another production run can differ slightly in shade.
• Walls: measure each tiled wall as its own area and leave out windows and doors, or take their area off with a second calculation.

What the estimate leaves out

• Cut tiles at the edges are counted as fractions of a tile by the area formula; in practice each cut uses a whole tile unless the offcut fits elsewhere. That is what the waste allowance is for.
• Grout, adhesive and underlayment are separate products with their own coverage. Their makers publish how much a bag covers for a given tile and joint size.
• Mosaic sheets are sold by the sheet: enter the sheet size as the tile size and the joint between sheets.