How to use this calculator
Measure the room at the floor, not at waist height, and measure both directions in two places. Walls are rarely parallel. If the two readings differ, use the larger one: you can cut a tile down, you cannot stretch one.
Put the long dimension in as the room length and the short one as the width. If the room is L-shaped — a kitchen with a pantry bumped out, a living room wrapping a chimney — switch the shape to L-shaped and enter the missing corner. The plan subtracts it from the top right, and the waste allowance goes up by two points because an L-shape puts a second set of edges into the field.
Tile size is the nominal size printed on the box: a 12 x 24 is really 11 7/8 x 23 7/8, and the grout joint makes up the difference. Use the nominal number. Then set the joint width you actually intend to use, because it changes the grout quantity by a factor of four between 1/16 and 1/4 inch.
Layout patterns and what they cost you
The pattern is the single biggest lever on how much tile you buy. Two floors of identical size can differ by 9 points of waste depending on nothing but the layout: on 400 square feet of the calculator’s 12 x 24 tile that is 30 boxes in a grid and 32 in a chevron, and the difference shows up as cuts around the perimeter. Here is what each one does to the order.
Grid
Every tile lines up with its neighbours in both directions. It is the cheapest layout to install and the cheapest to buy: 10% waste covers a rectangular room. The catch is that a grid is unforgiving of an out-of-square room — a wall that runs 3/4 inch off over 14 feet turns the last row into a visible taper.
Brick and offset
A half offset is the classic running bond. It hides small variations in tile size and in the room, and it costs about the same as a grid: 10%. Where the side being offset is longer than 15 inches, the installation standard ANSI A108.02 sets a maximum offset of 33% unless the tile manufacturer specifies otherwise, and many manufacturers now recommend a third. Long tiles have some inherent warpage, and a half offset lines the high edge of one tile up against the low edge of the next: lippage you cannot flatten out. Switch to a 1/3 offset and budget 12%.
Diagonal
Turning the field 45 degrees makes a small room look wider and turns every single perimeter tile into a cut. Budget 15%, and understand that the offcuts are triangles that only fit the opposite wall if the room is perfectly square. It is also slower to set, because you are working off two chalk lines that have no relationship to any wall.
Herringbone
The most expensive layout on this list at 17% and up. Every perimeter piece is a double cut at 45 degrees and each cut produces an offcut with two wrong angles. Herringbone also needs a 2:1 tile — 6 x 12, 4 x 8, 3 x 6 — because that is the only ratio where the pattern closes on itself. If your tile is 4 x 12 it is a 3:1 and has to be laid as a double herringbone, in pairs. Read the full breakdown in our guide to the tile waste factor by pattern before you commit to it.
Grout and thinset quantities
Grout is sold by the bag and the quantity follows the tile size and the joint width. Small tile has far more joint per square foot of floor: about 6 linear feet in every square foot of 3 x 6 tile, against 1.5 feet for a 12 x 24. The calculator works grout out the way Custom Building Products’ coverage charts for its Polyblend Plus grouts do: the joint’s width times its depth along every tile edge, at what a cubic foot of grout weighs. At a 1/8 inch joint that puts a 3 x 6 at 0.14 pounds per square foot and a 12 x 24 at 0.05, and a 1/4 inch joint roughly doubles both. Joints under 1/8 inch take non-sanded grout, which Custom sells in 10 pound boxes; wider ones take sanded, in 25 pound bags.
Thinset is simpler and people still get it wrong. The calculator assumes 95 square feet per 50 pound bag with a 1/4 by 1/4 inch square notch trowel. That is the top of the 80 to 95 square feet LATICRETE publishes for its 253 Gold mortar; the same data sheet gives 60 to 70 square feet with a 1/4 by 3/8 inch notch and tells you to back-butter tiles larger than 8 by 8 inches. The thinset line includes no back-buttering, and a deeper notch covers less, so if you are setting large tile, work the bag count out from the coverage printed on your bag rather than from the thinset line here.
Buy one more bag of thinset than you think you need and none of grout. Unopened thinset keeps if the bag stays dry — LATICRETE gives its 253 Gold a two year shelf life and warns that humidity shortens it — while opened grout hardens, and colour-matching a second bag from a different lot is a visible failure across a floor.
Common mistakes
- Measuring the room and ordering that number. A 168 square foot room needs 185 square feet of tile at the very least. Ordering 168 leaves you 17 square feet short on the last afternoon.
- Ignoring the box coverage. Boxes run from 8 to 24 square feet depending on the tile. Two boxes of a 15.5 square foot carton is not 31 square feet of usable tile once the cuts start.
- Buying from two dye lots. Check the lot number on every box at the store. A single box from a different run reads as a stain across the floor under raking light.
- Starting at a wall. Lay out from the centre lines so the cuts fall evenly. Our guide on how to lay out a tile floor walks through finding the working centre and killing sliver cuts before they happen.
- Forgetting the closet, the doorway and the hearth. Every one of them is extra square footage and extra cuts. Add them as separate rectangles.
- Skipping attic stock. Keep four to six full tiles. A cracked tile in year three is a twenty minute repair with a spare and a weekend with none.