How to use the tile layout and border cut calculator
- Enter the room length and width and the tile size along each direction. Use one unit, such as inches, for every measurement.
- Enter the grout joint. The 0.125 shown is an example, so use the joint you plan to leave.
- Set the smallest cut you will accept at a wall. Narrow strips are hard to cut and set, and many people avoid them. It can be at most half a tile.
- Choose centered on the room or start at one wall, then read the cut sizes, the whole and cut tile counts and the tiles to buy with your extra for breakage.
Formula
one tile and one joint = tile + joint
centered, m whole tiles: edge cut = (room - m x tile - (m + 1) x joint) / 2
largest m that keeps the edge cut at or above the smallest cut = floor((room - 2 x smallest cut - joint) / (tile + joint))
tiles to buy = (columns x rows) x (1 + extra) rounded up
From one wall, the whole tiles run out from the wall and the last tile is cut. When that last cut is narrower than your minimum, it is shared with the last whole tile so both end up half a tile or more.
A 147 by 110 inch room with 12 inch tile
Along the 147 inch length, one tile and one joint take 12.125 inches. The largest number of whole tiles that keeps each edge cut at 3 inches or more is floor((147 - 6 - 0.125) / 12.125) = 11, which leaves an edge cut of (147 - 132 - 1.5) / 2 = 6.75 inches at each wall.
Along the 110 inch width the same steps give 8 whole tiles and edge cuts of 6.4375 inches. The grid is then 13 by 10 tile positions, or 130, of which 11 x 8 = 88 are whole and 42 are cut. With 10% extra for breakage, 130 x 1.1 = 143 tiles to buy.
Starting at one wall instead gives the same answer here, because the leftover of 1.5 inches is below the 3 inch minimum and is shared with the last whole tile, which makes two cuts of 6.75 inches.
Why centering helps
If you start at one wall, the last row at the opposite wall can end up as a thin sliver, and the two walls look different. Centering puts a cut of the same size on both sides, so the room looks balanced and no cut is thinner than it has to be.
Dry fit a row of loose tiles with spacers along the length and width before you set any, and snap a chalk line through the center. The tool tells you the sizes to expect, and the dry fit shows you how the pattern meets doorways and thresholds.
Counting tiles
Every cut tile is counted as a whole tile because the offcut rarely fits anywhere else. The extra percentage is for breakage and future repairs. For the area and box count instead, use the Tile Calculator, and for wood or vinyl planks use the Plank Stagger Planner.
More layout tools
For other layout and fitting problems, try the Beam Deflection Calculator, Arch Template Calculator and Cut List Optimizer.
Assumptions and limits
- The room is a rectangle and the tile is a rectangle laid in straight rows with no offset pattern.
- The joint is the same in both directions.
- Cut tiles at the edges are counted as whole tiles.
- Obstacles such as cabinets, tubs and door openings are not removed from the layout.
Frequently asked questions
How big should the cut tiles at the wall be?
Many installers avoid cuts narrower than about half a tile, because narrow strips are hard to cut and keep straight. You can set your own smallest cut, up to half a tile, and the layout adjusts to respect it.
Should I start tiling in the center of the room?
Starting from the center line keeps the cuts equal at opposite walls and avoids slivers. Dry fit a row first to check how the pattern meets doorways, since that is usually the most visible edge.
Why does the tile count include cut tiles as whole tiles?
A cut tile uses one whole tile, and the offcut is often too small or the wrong shape to use elsewhere. Counting every position as a tile keeps the order safe.
Does the layout account for the grout joint?
Yes. The joint is added to the tile size to find how far each tile advances, and the joints are included when the edge cut is worked out.