Tile calculator

How the tile calculation works

The calculator divides the area you want to tile by the area one tile covers, adds your waste allowance, and rounds up, because you can’t buy part of a tile.

1. Area to tile = length × width, minus any areas you subtract.
2. Area of one tile = (tile length + grout joint) × (tile width + grout joint).
3. Tiles = area to tile ÷ area of one tile.
4. Tiles with waste = tiles × (1 + waste %), rounded up to a whole tile.
5. Boxes = tiles with waste ÷ tiles per box, rounded up to a whole box.

The tile area is converted to the room’s units first: square inches ÷ 144 = square feet, and square millimeters ÷ 1,000,000 = square meters.

Worked example

A 12 ft × 10 ft floor, 12 in × 12 in tiles, 1/8 in (0.125 in) grout joints, 10% waste and 20 tiles per box:

1. Area: 12 × 10 = 120 sq ft.
2. One tile with its joint: 12.125 in × 12.125 in = 147.02 sq in, and 147.02 ÷ 144 = 1.0209 sq ft.
3. Tiles: 120 ÷ 1.0209 = 117.54.
4. With 10% waste: 117.54 × 1.1 = 129.29, rounded up to 130 tiles.
5. Boxes: 130 ÷ 20 = 6.5, rounded up to 7 boxes (140 tiles).

In metric, a 3 m × 4 m floor with 300 mm × 300 mm tiles and no grout joint is 12 m² ÷ 0.09 m² = 133.33 tiles. With 10% waste that is 146.67, so you would buy 147 tiles.

A real project

I retiled my bedroom, which is 10 ft by 12 ft (120 sq ft), with large 3 ft x 3 ft tiles (9 sq ft each).

First I used the area method. 120 sq ft divided by 9 sq ft is 13.33 tiles. Adding 10% for cuts and breakage gives 14.67, so I rounded up and bought 15 tiles.

That turned out to be too few. With 3 ft tiles, the 12 ft side fits exactly 4 tiles, but the 10 ft side needs 3.33, which means 4 tiles with the last one cut. So the layout needed 4 x 4 = 16 tiles even before anything went wrong. Then one tile broke, and another was damaged. I reused part of the damaged one elsewhere, but I still ended up using 17 tiles in total and had to buy 2 more.

The area calculation counts every leftover piece as usable. In practice, with large tiles, you can’t always use the offcuts. Next time I would count whole tiles along each wall first, then add a spare tile or two for breakage.

The calculator on this page gives you the area-based number. Use it as your starting point, then check it against your actual layout.

Assumptions and limits

• Waste allowance. The default is 10% for a straight layout. The layout menu suggests 15% for diagonal and herringbone layouts, which need more cuts. These are suggestions: change the figure to suit your room.
• Rounding. Tiles are rounded up to a whole tile and boxes up to a whole box. The breakdown shows the unrounded numbers so you can check each step.
• Based on area. The count doesn’t plan individual cuts, so rooms with many corners, pipes or angled walls may need more waste.
• One tile size. For patterns that mix sizes, do one calculation per size.
• Not included: adhesive or thinset, grout, spacers, trim and edging, backer board, underlayment and leveling compound.

Practical tips

• Buy from the same batch. Color and shade can vary between production runs. Check that the batch or lot number matches on every box before you start.
• Keep spares. Store a few leftover tiles for future repairs. The same tile can be hard to find a few years later.
• Very small or very large tiles may need more waste. Large tiles leave bigger offcuts. Mosaics usually come on mesh sheets, so enter the sheet size as the tile size.
• Use the tile’s actual size. The size on the label is often a rounded, nominal size. Measure a tile and use that if it’s different.
• Check the box label. Many boxes state the area they cover. Comparing that with the tiles per box is a quick check on your numbers.