Set out a tiled floor or wall before you spread any adhesive. It works out how many full tiles you need, the exact size of every perimeter cut, and — when a cut comes out too thin to survive being cut — how far to move your starting point so both walls get an equal, workable cut instead of one sliver. Scaled plan and grouped cut list, ready to print. Runs entirely in your browser, nothing is uploaded.
Because you usually cannot cut it. A sliver that narrow snaps on the wet saw, crumbles at the glaze, and the ones that survive look like a mistake for the life of the floor. Most tilers refuse anything under about a third of the tile, and never go below roughly 30–50 mm on a floor tile. That is what the "minimum acceptable cut" box is for: set it to what you are actually willing to fit, and the tool tells you whether your layout produces it.
If you start with a full tile hard against one wall, all the leftover ends up at the far wall — sometimes as a 20 mm strip. Move the whole field along by a set amount and that leftover gets split between the two walls, so instead of one full tile and one sliver you get two half-decent cuts. The tool searches every possible start position along one tile pitch, finds the one that makes the narrowest cut in the room as wide as possible, and gives you two numbers: how far to shift, and where to snap your first full tile line measured from the wall. If even the best position cannot reach your minimum, it says so rather than pretending otherwise — at that point you change the tile size, the joint width, or you accept the cut. The same rule drives the "centred" start option: a room has two symmetric layouts, one with a tile straddling the centre line and one with a joint on it, and the tool picks whichever gives the wider perimeter cut.
Sometimes. The cut list shows a conservative "pieces per tile" figure — how many identical border pieces can be sawn from one full tile, capped at four, and it ignores the blade kerf and the tiles you will break learning the saw. Two totals are given: one assuming a whole tile per cut piece (safe, what most merchants will quote you) and one assuming you nest the cuts. Order the first unless you are confident and the tile is expensive. Directional or heavily patterned tiles cannot be nested at all, because the offcut ends up facing the wrong way.
It assumes the room is a true rectangle with square corners — it is not. Walls bow, corners run out, and a 4 m wall that is 15 mm out of parallel will eat your border cut at one end. Measure both ends of every wall and plan against the worst case. It also ignores door thresholds, thresholds strips, pipe penetrations, floor waste falls, diagonal and herringbone patterns, and anything to do with substrate, movement joints or adhesive coverage. It is a setting-out aid, not a specification.