The formula behind the calculator
A tile count is the area to cover divided by the area one tile covers, plus an allowance for cuts and breakage. The calculator counts each tile with its grout joint, because the joint is part of the space every tile takes up.
Tiles = (area - parts left out) x (1 + waste) / ((tile length + joint) x (tile width + joint))
A 10 by 12 foot floor is 120 square feet. A 12 by 12 inch tile with a 1/8 inch joint takes up 12.125 by 12.125 inches, or about 1.02 square feet. That gives 118 tiles for the floor itself and 130 with a 10% allowance. Sold 10 to a box, that is 13 boxes and 12 spare tiles.
How much extra to allow
Extra tiles cover the cuts along walls and around fixtures, tiles that break and the pieces you keep for later repairs. The allowance depends mostly on the layout:
| Layout | Typical allowance |
|---|---|
| Straight lay in a simple room | about 10% |
| Large, square room with few cuts | 5 to 10% |
| Diagonal or brick-offset layout | about 15% |
| Herringbone, chevron or many corners and fixtures | about 20% |
Large-format tiles waste more per cut, because an offcut that is too small to reuse is a bigger share of the tile. Check the manufacturer's guidance for the tile you choose.
Measuring the area
- Measure the full length and width of the space, wall to wall, and enter them in feet or metres.
- For an L-shaped room, split it into two rectangles, run the calculator for each and add the results, or measure the bounding rectangle and leave out the missing corner.
- Use Leave out for areas that will not be tiled, such as kitchen cabinets, an island, a tub or a shower tray.
- For a wall, enter the width and the height of the tiled section instead of the floor length and width.
Boxes, lots and spares
Tile is usually sold by the box, and the label states how many tiles or how many square feet it holds. Enter the tiles per box to get a whole number of boxes. If the label only gives square feet per box, divide that by the area of one tile to get the count.
Tiles from different production runs can differ slightly in shade and size. Buy all the boxes from the same lot, and keep a few spare tiles in case one cracks later; a matching tile can be hard to find once a line is discontinued.
Working out the cost
The calculator does not hold price data. Enter the price you were quoted per box, or per square foot or square metre, to see the tile cost for the quantity you need. Adhesive or thinset, grout, trim pieces, underlayment and installation labour are separate costs.
When to call a tile installer
A professional installer checks that the floor is flat and stiff enough for the tile, plans the layout so cuts land in sensible places, and handles waterproofing in wet areas. If you would rather have the job done for you, compare local flooring installers and ask each one to measure and quote the same layout.