Tile count is area divided by tile size, and then the waste allowance does the real work. Layout pattern drives waste more than room shape does, and running short mid-job means a different dye lot.
Waste by layout
A straight grid against square walls wastes about 10 percent. Turn it 45 degrees and every perimeter tile is a cut — 15 percent. Herringbone cuts the most and needs 20.
Small rooms waste proportionally more than large ones because the perimeter is a bigger share of the area. A bathroom floor can justify 15 percent even laid straight.
Thinset depends on the trowel, not the tile
A 50 pound bag covers roughly 85 square feet with a quarter-inch square-notch trowel. Move to a half-inch notch for large-format tile and coverage drops to around 45 square feet.
Large-format tile — anything over 15 inches on a side — also needs back-buttering, which uses more again. Buy an extra bag rather than stopping mid-floor with mixed thinset going off in the bucket.
Grout varies more than any other number here
Grout quantity depends on tile size, joint width and tile thickness together. Twelve-inch tile with eighth-inch joints uses about a quarter pound per square foot. Mosaic sheets with the same joint width can use three times that.
Use the figure above as a starting point and check the coverage chart on the grout bag against your actual tile size — it is one of the few places manufacturers publish genuinely reliable numbers.
Check the lot number on every box
Shade variation between production lots is normal and visible. Confirm every box in the order carries the same lot number before the delivery driver leaves.
Open several boxes and mix tiles as you lay, the same way you would with pavers. It turns batch variation into texture instead of patches.
Layout starts from the middle, not the wall
Starting at one wall and working across guarantees a sliver of tile at the far end, and it will be at the most visible wall as often as not.
The standard approach is to find the centre of the room, dry-lay a row each way, and shift the layout so the cut tiles at both ends are equal and as large as possible.
Where the room is not square — which is most rooms — the layout is set from the most visible straight line, usually the longest wall or the sightline from the door, and the discrepancy is pushed to where it will not be seen.
Movement joints
Tile assemblies need somewhere to move. A soft joint — caulk or a proprietary profile rather than grout — is required where the tile meets a wall, at changes of plane, and at intervals across a large floor.
Grouting a floor tight to the walls on all sides gives thermal and structural movement nowhere to go, and the result is tenting, where tiles lift off the floor in a ridge.
It happens most often on large floors, over heated slabs, and in sunrooms. The perimeter joint hidden behind the baseboard costs nothing and prevents it.