Tile Layout Calculator

A tile count tells you what to buy. What decides whether the floor looks right is the width of the cuts at the edges, and that is set before the first tile goes down. Start tight against a wall and everything left over lands in one strip at the far side — often a sliver too narrow to cut cleanly. Centre the layout and the remainder splits in two. And when even the centred cut comes out narrow, shifting the whole grid half a tile turns two bad edges into two good ones, for the same number of tiles.

Edge cuts: 11 1/2" across, 17 11/16" along Centred layout: the remainder is split evenly, so both edges of each axis take the same cut. Every wall gets the same treatment, which is what makes a centred floor look deliberate.
Full tiles: 8 × 5 Each tile occupies 12 1/8" across and 24 1/8" along once the 0.125" joint is added. The joint is not free space — over 8 tiles it accumulates to 1".
If you started at a wall: 10 7/8" at the far side Wider than a third of a tile, so a wall-start layout is defensible here — particularly if one wall is the visible one and the other is under cabinets.
The other centred layout: 5 7/16" across, 5 5/8" along Centring has two versions half a module apart — a joint on the centre line, or a tile centred on it. This layout uses the joint-centred option across the width because it gives the wider cut; the other would leave 5 7/16". Checking both costs nothing and it is the step almost everyone skips.
Tiles to buy: 71 tiles 130.0 ft² of floor plus 10% waste. A straight layout wastes around 10%; a diagonal layout wastes 15% or more because every perimeter cut is a triangle. Buy the whole job in one batch — tile is made in dye lots and two lots do not match.
Put the cuts where nobody looks: Not at the doorway A centred layout is symmetrical, not automatically correct. In a room with one visible entrance, biasing the grid so full tiles land at the doorway and the cuts go under the vanity or against the least visible wall usually looks better than perfect symmetry.
Check the room is square first: 3-4-5 Rooms are rarely square, and a layout referenced from a wall that is not straight puts a tapering cut down the opposite side. Snap chalk lines from the centre, check them at right angles with a 3-4-5 triangle, and lay to the lines rather than to the walls.
Dry lay the first two rows: Before any adhesive Everything above is arithmetic on nominal dimensions. Real tiles vary, particularly rectified against non-rectified stock, and lippage accumulates. Two dry rows across the longest dimension confirm the layout before it becomes permanent.

The joint is part of the module

A twelve inch tile with an eighth inch joint occupies twelve and an eighth inches. That is the module, and it is what the room divides by.

Over a short run the difference is invisible. Over twenty courses the joints add up to two and a half inches — a fifth of a tile — which is quite enough to turn a comfortable edge cut into a sliver, or to move a cut from one side of a doorway to the other.

This is the same accumulation that catches people out with deck boards, running the other direction: there the gaps meant fewer boards than expected, here the joints mean fewer tiles across the room than the bare division suggests.

Use the module for layout arithmetic and the tile size for nothing except ordering.

Centring, and the half-tile shift

Starting from a wall gives one clean edge and puts the entire remainder at the opposite side. When that remainder happens to be most of a tile the result is fine. When it is an inch, it is a fragile strip that is hard to cut and impossible not to notice.

Centring splits the remainder between both edges, so each side takes half. That is usually better, and it is what most guidance stops at.

The step beyond is that centring has two versions: a joint on the centre line, or a tile centred on it. They differ by half a module, and they produce different edge cuts. Where one gives a sliver, the other usually gives a comfortable cut.

The working rule is to aim for edge cuts of at least half a tile. If the layout you have does not give that, shift it half a module and check the other version. It costs nothing, uses the same number of tiles, and it is the single biggest difference between a floor that reads as planned and one that reads as improvised.

Symmetry is not the goal

A perfectly centred layout is symmetrical about both axes, which sounds like the right answer and often is not.

Most rooms have one direction people arrive from and look along. Putting full tiles at the doorway and pushing the cuts to the far wall, under a vanity, or behind a door swing, generally looks better than a symmetrical layout with two mediocre cuts in plain sight.

The same logic applies to which axis gets the compromise. A long narrow room reads along its length, so the cuts along the long walls matter more than the ones at the ends.

And before any of it, check the room. Rooms are not square, and a grid referenced from a wall that runs out by half an inch over twelve feet puts a tapering cut down the opposite side that no layout arithmetic will fix. Snap lines from the centre, square them with a three-four-five triangle, and lay to the lines.

What this is based on

Layout module — tile dimension plus grout joint width
Common practice: edge cuts no narrower than half a tile, achieved by shifting the grid half a module

A layout estimate on nominal dimensions. Real tiles vary, particularly non-rectified stock, and rooms are rarely square. Dry lay two rows across the longest dimension before committing to adhesive. It does not address substrate preparation, movement joints or waterproofing, all of which matter more than the layout.

Frequently asked questions

Should I start tiling from the centre or a wall?

From the centre in most rooms. Starting at a wall puts the entire remainder in one strip at the far side, which is often too narrow to cut cleanly. Centring splits it between both edges so each cut is twice as wide.

What if the centred layout still gives a narrow cut?

Shift the whole grid half a tile. Centring has two versions — a joint on the centre line or a tile centred on it — and they differ by half a module. Where one gives a sliver the other usually gives a comfortable cut, for the same number of tiles.

How narrow is too narrow for an edge cut?

Aim for at least half a tile. Below about a third, cuts are fragile, hard to make cleanly, and visibly wrong from across the room even to people who could not say what is bothering them.

Does the grout joint change the tile count?

Yes. A 12 inch tile with an eighth inch joint occupies 12.125 inches, and over twenty courses that adds up to two and a half inches — a fifth of a tile. Use the module, not the tile size, for layout arithmetic.

How much waste should I allow?

Around ten percent for a straight layout and fifteen or more for a diagonal one, because every perimeter cut on a diagonal is a triangle with an unusable offcut. Buy the whole job in one batch — tile is made in dye lots and two lots do not match.