Tile Calculator
Enter your room size and tile dimensions to get the number of boxes to buy. Waste is set automatically by layout — a diagonal pattern needs nearly twice the offcut allowance of a straight one.
Buy by the box, not the tile
Tile is sold in boxes and stores rarely split them. So the real answer is never "you need 78 tiles" — it is "you need 14 boxes", and this calculator rounds up for you.
Check the tiles per box figure on the label, because it varies enormously. A box of 12×24 might hold 6 tiles; a box of 3×6 subway might hold 40. Some tile is sold by square feet per box instead of piece count — in that case divide box coverage by the square feet per tile shown in the output to get the piece count.
Waste is set by the layout, not by carefulness
The waste allowance is not padding for mistakes. It is the tile you physically cannot use because it ends up as an offcut of the wrong shape.
Straight or stacked — 10%. Cuts happen at the perimeter, and the piece cut off one end often fits the opposite end.
Offset or brick — 12%. The staggered start of each row wastes slightly more.
Diagonal 45° — 18%. Every tile at the perimeter becomes a triangle, and triangles rarely pair up.
Herringbone or chevron — 22%. Every piece is cut at an angle and there is almost no reusable offcut anywhere.
Add another 5% for a room with alcoves, angled walls, or many doorways, and another 5% if the tile is being discontinued and you want spares stored away.
Keep the leftovers
The spare tiles output matters more than it looks. Tile production runs vary in shade, and lines are discontinued constantly. If a tile cracks in three years and you have none left, matching it is usually impossible — the realistic repair becomes retiling the whole room.
Two or three spare tiles in the garage is cheap insurance. Also check that every box you buy carries the same lot or shade number; mixing lots produces a visible colour band across the floor that only appears once it is all down.
Thinset and grout are estimates
The adhesive and grout figures are approximations, and both are genuinely hard to predict.
Thinset coverage depends on your trowel notch size, which depends on tile size and how flat the substrate is. A 50 lb bag covers roughly 60 to 95 square feet — this calculator uses a conservative 70.
Grout depends on joint width, tile size, and tile thickness together. A narrow 1/16" joint on large-format tile uses very little; a 3/16" joint on small mosaic uses many times more. Use the manufacturer's coverage chart on the bag for anything beyond a rough shopping estimate.
Neither figure includes what you need for a backer board, waterproofing membrane, or levelling compound.
Frequently asked questions
How much extra tile should I buy?
Ten percent for a straight layout, about 12 percent for offset or brick, 18 percent for a 45-degree diagonal, and 22 percent for herringbone. Add another 5 percent for rooms with alcoves or many doorways. The allowance covers offcuts you cannot reuse, not mistakes.
How many tiles are in a box?
It varies by tile size — a box of 12×24 might contain 6 tiles while a box of 3×6 subway holds 40. Always check the label. Some tile is sold by square feet per box rather than piece count, in which case divide the box coverage by the square feet per tile.
Why does a diagonal layout need more tile?
Because every tile meeting a wall is cut into a triangle, and triangular offcuts rarely fit anywhere else. In a straight layout, the piece cut from one end of a row often fits the opposite end, so far less is thrown away.
How much thinset and grout do I need?
Roughly one 50 lb bag of thinset per 70 square feet, though coverage ranges from about 60 to 95 depending on trowel notch size. Grout varies far more, driven by joint width and tile size together. Both figures here are shopping estimates — use the coverage chart on the bag for a real order.
Should I keep leftover tiles?
Yes, always. Tile lines are discontinued frequently and shade varies between production lots, so a cracked tile years later often cannot be matched. Keeping two or three spares turns a whole-room retile into a single-tile repair. Also check that all your boxes share the same lot number before starting.