TradesHow this works
Tile fills a room as a grid of full tiles with a cut row at the edges. Working from the tile size plus the grout joint, the tool counts the full tiles each way and measures the leftover cut at the walls. That cut is what makes or breaks the look.
If a flush start leaves a cut wider than half a tile, it recommends starting at the wall, which is the least cutting. If the leftover would be a thin sliver, it recommends centering the field so both edges get equal, cut-friendly borders instead. Either way, dry-lay a row with spacers before you set anything, because a half-tile shift is what turns a sliver into a clean border.
Common questions
Should I start tile at a wall or in the center?
It depends on the leftover cut. Starting flush at a wall is the least cutting and gives a full tile at the start, but the far wall gets whatever is left, which can be an ugly sliver. Centering the field splits that leftover into two equal borders on both sides, which is worth it when a flush start would leave a cut narrower than about half a tile.
What is a tile sliver and why avoid it?
A sliver is a very thin cut tile at an edge, narrower than about half a tile or under a couple of inches. It looks unbalanced against the wall, and a thin strip of tile is fragile and hard to cut cleanly. The fix is to shift the layout, usually by centering the field, so the edge cuts come out wider and even on both sides.
How does grout width affect the layout?
Every joint adds the grout width to the run, so a wider joint spreads the field and can pull an edge tile just over or under a full width. It is small per joint but it adds up across a room, which is why you dry-lay a row with spacers before setting anything, rather than trusting the tile size alone.
Sources: Layout geometry (evergreen): tile plus grout joint, edge cuts, sliver avoidance. Engine version 1.0.0. Risk tier 1.