Tile box coverage is the area one box covers as sold — and it is the only coverage figure that should enter a box count. Pattern waste is everything the pattern consumes beyond the net area: edge cuts, pattern repeats and unusable offcuts. The two are multiplied, not added as a single percentage, and the result is rounded up to whole boxes.
Label coverage first
Read the box label for the product you will buy: a box that covers 12.5 ft² is a different purchase from one that covers 10 ft², even for the same tile size, because pack counts differ. On 100 ft² net at 10% waste, order area is 110 ft², which is 9 boxes at 12.5 ft² (purchased 112.5 ft²). Change the label figure and the box count changes — that sensitivity is a feature, because it stops a generic “tiles per square foot” guess from masquerading as a product calculation.
Pattern waste without a universal rate
Straight layouts commonly need less waste than diagonal, herringbone or offset patterns, and irregular rooms need more than rectangular ones. No universal rate is asserted here: set waste for the actual pattern and room shape, keep a box of spares for future repairs with a matching dye lot, and run the figures in the Tile Calculator before ordering. For tile-count (rather than coverage) layouts with mixed sizes or grout-joint modelling, a separate tile-by-tile count is needed — the coverage mode does not pretend to be that calculation.