Measure the Room Before Choosing Tiles
Measure the length and width of the floor at its widest points, in feet or metres, and multiply the two figures for the gross area. Rooms rarely form a perfect rectangle, so taking three measurements across each direction and using the largest keeps the estimate on the safe side. Alcoves, closets, and doorways that receive tile need their own rectangle added to the total. Doorways that end at a threshold can be measured to the threshold line. Subtracting fixtures such as a bathtub or a built-in cabinet avoids paying for tile that will never be laid, but only when the fixture sits on the subfloor rather than over the tile.
Convert Tile Size to Coverage
A tile sold as 12 by 24 inches covers 288 square inches, or 2 square feet, because 12 times 24 equals 288 and 144 square inches make one square foot. A 60 by 60 centimetre tile covers 0.36 square metres. Dividing the room area by the coverage of one tile gives the tile count, so a 120 square foot floor with 2 square foot tiles needs 60 tiles before waste. Metric and imperial sizes are rarely exact, and a nominal 12 inch tile often measures 11.8 inches. Using the printed nominal size is fine for estimating, while the actual size matters when the layout is tight.
Set a Waste Allowance by Layout
Straight lay installations with few cuts run on a 10 percent allowance. Diagonal layouts, herringbone patterns, and rooms with many corners push that to 15 percent, and small tiles in a busy pattern can justify 20 percent. The allowance covers breakage, miscuts, and future repairs from the same dye lot. Adding waste to the tile count rather than to the room area keeps the arithmetic clear: 60 tiles at 15 percent becomes 69. Ordering a spare box beyond the calculated waste is common practice for floors that may need a patch years later, since a discontinued tile cannot be matched. Keeping that spare from the same batch matters more than the extra cost, because a later purchase comes from a different production run and a close match is often visible in daylight.
Turn Tiles into Boxes
Tile is sold by the box, and the coverage printed on the carton is the number that matters. A box covering 15 square feet means a 120 square foot floor with a 15 percent allowance needs 138 square feet, or 9.2 boxes, rounded up to 10. Sellers sometimes quote a price per square metre and ship boxes of fixed coverage, so the figure printed on the carton is worth reading twice before the order is confirmed. Boxes from different production runs can differ slightly in shade and calibre, so ordering the whole quantity at once avoids a visible seam between batches. Checking the calibre number printed on each carton helps when boxes arrive together, because tiles in the same calibre group share dimensions closely enough to lay without lippage.
Grout Lines, Borders, and Cut Pieces
Grout joints of 3 millimetres add a small amount of coverage per tile, which matters with small formats: a 100 millimetre tile with a 3 millimetre joint gains about 6 percent coverage. For large format tile the effect is negligible. A border or accent band is calculated along its own linear run rather than folded into the field tile count. Cut pieces at the perimeter are taken from full tiles, and a row narrower than about a third of a tile usually looks better centred, which increases the number of cuts and the waste allowance. Checking the layout with a dry run of a few rows exposes awkward slivers before the adhesive is mixed.