Tile Calculator

Using the tile calculator

1. Enter the area length and area width of the surface you will cover. Each has its own unit menu (mm, cm, m, in or ft).
2. Enter the tile width and tile length, again in any of those units. Tile sizes are usually printed on the box and in the shop listing.
3. Set the gap size, the width of the joint between neighbouring tiles. It defaults to 0.3 in; use 0 for butt-jointed tiles.
4. Choose a waste percentage. The default is 5%, and it must be a whole number.
5. Optionally add the tiles per box and the price per box to turn the tile count into boxes and a total.

The results list the area covered, the number of tiles needed (waste included), the number of boxes (rounded up), and the total price. A price on its own, with no box size, gives a total of zero because there are no boxes to charge for.

How the number of tiles is calculated

Each tile effectively occupies its own size plus one joint on each of two sides. The calculator divides the area by that footprint, adds the waste allowance and rounds up to a whole tile.

tiles = ⌈ area ÷ ((tile width + gap) × (tile length + gap)) × (1 + waste ÷ 100) ⌉

boxes = ⌈ tiles ÷ tiles per box ⌉ total price = boxes × price per box

The brackets ⌈ ⌉ mean "round up". Rounding up is deliberate: you cannot buy part of a tile, and a count that falls short by one tile means a second trip to the shop and possibly a different production batch.

Worked examples

A bathroom floor in US units. The floor is 10 ft by 8 ft, so the area is 80 ft², or 11,520 in². The tiles are 12 in by 12 in with a 1/8 in (0.125 in) joint and 10% waste.

• Footprint of one tile: (12 + 0.125) × (12 + 0.125) = 147.016 in².
• Tiles before waste: 11,520 ÷ 147.016 = 78.36.
• With 10% waste: 78.36 × 1.10 = 86.20, which rounds up to 87 tiles.
• Sold in boxes of 10: 87 ÷ 10 = 8.7, so 9 boxes. At $38 a box that is $342.

A kitchen in metric units. The floor is 4.2 m by 3.1 m (13.02 m²). The tiles are 600 mm by 300 mm with 3 mm joints, and you allow 8% waste. One tile plus joint covers 0.603 × 0.303 = 0.1827 m², so 13.02 ÷ 0.1827 = 71.26 tiles, or 76.96 with waste. Order 77 tiles; at 6 per box that is 13 boxes, and at $54 a box the total is $702.

Choosing the gap and the waste allowance

The joint width depends on the tile and the installation method. Precisely cut (rectified) porcelain is often laid with joints of 1.5 to 3 mm, standard glazed tiles commonly use 3 to 5 mm, and rustic or hand-made tiles can need 10 mm or more. Check the manufacturer's instructions, because a wider joint means fewer tiles for the same floor.

Waste covers cuts at the edges, breakage and mistakes. Common allowances are about 5% for a plain rectangular room with a straight layout, 10% for rooms with many cut-outs or for larger tiles, and 15% or more for diagonal, herringbone and other patterns where many tiles are cut at an angle. It also pays to keep a few spare tiles for future repairs, since the same design may be discontinued.

The calculator only accepts a whole-number waste percentage. For a figure such as 7.5%, round up to 8%.

Layouts, shapes and irregular rooms

The count depends on area, not on the order in which tiles are laid, so straight, brick-bond and other layouts all give the same base figure. The pattern shows up through the waste allowance, which is why diagonal and herringbone floors need more.

Every tile is treated as a rectangle of the width and length you enter. For square and rectangular tiles that is exact. Round, hexagonal or irregular tiles leave gaps that cannot be tiled, so use the dimensions of the tile's bounding rectangle, add extra waste and confirm the coverage per box with the supplier.

For L-shaped or irregular rooms, split the floor into rectangles and add them up, or use the square footage calculator, which handles a two-section room. Subtract large fixed items such as a bath or kitchen island only if you will not tile beneath them.

Buying tips

• Buy everything in one go and from one batch. Shade and size can vary slightly between production runs.
• Check the box coverage as well as the piece count. Suppliers often print the square metres or square feet per box, which should match your tiles per box times the tile size.
• Remember adhesive and grout: they are bought by the area, not by the tile.
• For walls, remember that the height of the tiled area counts too. The paint calculator works out wall areas in a similar way, and the brick calculator does the same job for masonry.