How the Tile Layout Planner works

A straight tile layout that is the same at both walls can only be centred in two ways: with a tile sitting across the centreline of the room, or with a grout joint on it. This tool works out both for each direction of the room and recommends the one that leaves the larger piece at the walls. A row that ends in full tiles counts as the largest piece of all.

Everything is worked from the centreline outwards, one half of the room at a time, so the two cuts on an axis are always equal. For a 96 in wall, 12 in tile and a 1/8 in joint, a joint on the centreline gives 6 full tiles and cuts of 11 9/16 in at each wall; a tile on the centreline gives 7 full tiles and cuts of 5 1/2 in. Each answer can be checked by adding it back up: full tiles, cuts, joints and any gap at the walls must equal the room dimension. The tests behind this tool repeat that sum for thousands of random rooms.

The two layouts are half a module apart, so their cuts differ by half a tile plus half a joint. That is why, with the threshold at half a tile, one of them always clears it: either its cut is at least half a tile or it has no cut at all.

The start line is the centre of the grout joint nearest the middle of the room. The drawing is built from the same list of pieces as the figures: each joint is drawn at its position along the wall, and the cut tiles are shaded. When the tiles are too small to show at the scale of the drawing, the joints are left out and only the cut tiles are drawn.

Where the half-tile test comes from

The geometry above is arithmetic. What counts as a good layout is guidance, and it is taken from these sources:

• ANSI A108.02, sections 4.3.1 and 4.3.2, as quoted by the Ceramic Tile Education Foundation: tile areas are to be centred and balanced where that is possible, and cuts smaller than half a tile should usually be avoided. The standard itself was not read for this tool. The National Tile Contractors Association's TileLetter summarises ANSI A108.02 section 4.3 the same way and reports that the TCNA Handbook suggests the same.
• Daltile's floor and wall installation guides: lay a dry row out from the centre line, and if the cuts at the walls are smaller than half a tile, snap a new line half a tile closer to the wall. That half-tile shift is, in effect, the move from one of the two layouts here to the other; this tool works it out as half a tile plus half a joint.

The flag in this tool is set to 50% of a tile for that reason, and you can change it. As quoted, the standard qualifies both points: centre the layout where possible, and usually avoid the small cuts. TileLetter, relaying the TCNA Handbook (which was not read for this tool), lists cases where a centred layout may not be the best choice: a focal point or decorative feature that the layout should line up with, a room whose shape makes centring impossible in every direction, a layout that runs on through several spaces, and the effect on waste. Those are judgement calls this tool does not make for you.

The gap at the wall

By default the cut tile is measured right to the wall and no grout joint is assumed there. If you enter a gap, that much is left empty at each wall and the layout is worked out again for the shorter span. Usually that makes each cut narrower by the gap, but not always: on a 96 7/8 in wall with 12 in tile and a 1/8 in joint, no gap gives 8 full tiles and no cuts, and a 1/4 in gap gives 6 full tiles and cuts of 11 3/4 in. On a 97 1/4 in wall the better start moves: a tile on the centreline with cuts of 6 1/8 in without a gap, a joint on the centreline with cuts of 11 15/16 in with one. Enter the gap; do not subtract it from a result by hand. Daltile's guides fit the perimeter tiles leaving a 1/4 in gap between tile and wall; use the figure in the instructions for your own tile and setting material.

If the full tiles stop short of the wall by less than one joint width, the tool reports that leftover instead of a cut. When a row comes out as full tiles wall to wall and the gap box was left blank, the result is shown as a warning until you enter a gap, or 0 to confirm there is none, because that row is the one a gap changes most.

Joint width, as arithmetic only

When even the better layout leaves a cut under your threshold, the tool shows what a different joint width would do: narrowing every joint makes each cut wider by half the number of joints in the row times the change, and one particular joint width makes a whole number of tiles fit with no cuts. Only joints from 1/16 in to 1/2 in are shown, and nothing is shown when the sum lands outside that range. The lower end is TileLetter's figure for the smallest joint ever recommended; the upper end is this tool's own cut-off, not a rule. These are sums, not advice. Whether a joint of that width suits your tile is for the tile and grout instructions to say.

What this does not cover

• Brick, offset, herringbone and diagonal patterns. Only a straight grid with the joints lined up both ways.
• Rooms that are out of square, L-shaped rooms, and fixed features such as a tub, a niche or a doorway.
• How many tiles to buy. The counts are the pieces in the layout; breakage, offcut reuse and a waste allowance are not included.
• Tiles that vary in size. Every tile is taken to be the size you enter.

This tool cannot be published unless it reproduces every example below. 14 were worked by hand from the cited rule.