How to calculate it yourself
Tiles per ft² = 144 ÷ (length in inches × width in inches). Total tiles needed = (room area in ft² × 1.10 waste) × tiles per ft², rounded up. For irregular shapes, break the room into rectangles and add the totals. Mosaic sheets cover ~1 ft² each but the individual tile count varies by mesh layout.
Common scenarios
Bathroom floor, 12×12 tile
A 5×8 ft bathroom (40 ft²) at 1 tile per ft² + 10% waste = 44 tiles. At 10 tiles per box (typical for 12×12), that is 5 boxes — buy the 5th box even though box 5 is only ~80% used. Returning leftover tile is harder than buying short.
Subway tile backsplash, 3×6
A 12-foot kitchen run × 18 inches tall = 18 ft². 18 × 8 tiles per ft² × 1.15 (15% for cuts and corners) = 166 tiles. At 22 tiles per box, that is 8 boxes.
Large-format 24×24 floor
A 200 ft² living area × 0.25 tiles per ft² × 1.10 = 55 tiles. At 4 per box, that is 14 boxes. Watch the substrate — large-format needs an extra-flat floor (no more than ⅛ inch deviation in 10 feet) to avoid lippage.