Tile Calculator

How to Use the Tile Calculator

Tiling is three separate purchases that people usually make as one guess: the tiles themselves, the grout that fills the joints between them, and the adhesive under them. This calculator works out all three, and it derives the grout from the actual geometry of your joints rather than from a chart.

1. Measure the floor or wall. Length by width. Tile a wall and a floor separately, since they usually take different tiles and certainly different waste allowances.
2. Enter the tile size and the box count. Both are on the box. Tile dimensions are nominal — a '12 by 24' is usually a millimetre or two under, which is what the grout joint absorbs.
3. Set the joint width and tile thickness. These drive the grout calculation. An eighth of an inch is the common floor joint; a sixteenth is used for rectified tile.
4. Pick the trowel notch. Adhesive coverage depends far more on the notch size than on anything else — a half-inch notch uses more than twice what a quarter-inch notch does.

Everything is computed in your browser and nothing is stored.

Tile and Grout Formulas

Tiles are simple division. Grout is where the real geometry is, and it is worth seeing rather than taking on trust.

The grout formula follows from one idea. Each tile, together with its share of the joints around it, occupies a cell measuring (A + w) by (B + w). The tile itself fills A by B of that cell, and everything left over is grout. Multiply that fraction by the depth of the joint and you have a volume.

One honest caveat: manufacturer coverage charts consistently call for fifty to seventy per cent more grout than this geometry implies, because mixing waste and what stays on the float are real losses that no formula captures. Treat the calculated figure as the floor and buy to the bag chart.

Example

Worked example one: a 12 ft by 10 ft floor in 12 by 24 inch tile. The area is 120 square feet and each tile covers (12 × 24) ÷ 144 = 2 square feet. A 10% allowance takes the requirement to 132 square feet, so 132 ÷ 2 = 66 tiles. At eight tiles a box each box covers 16 square feet, and 132 ÷ 16 = 8.25, so you buy 9 boxes covering 144 square feet — 24 square feet spare. At $51.20 a box that is $460.80.

Now the grout. The cell is (12 + 0.125) × (24 + 0.125) = 12.125 × 24.125 = 292.515625 square inches, against a tile of 288. The difference is 4.515625, so the grout fraction is 4.515625 ÷ 292.515625 = 0.0154372, or 1.54% of the surface.

Per square foot that is 144 × 0.0154372 × 0.375 = 0.8336 cubic inches. Over 132 square feet it is 110.04 cubic inches, which is 0.0637 cubic feet, or 7.51 lb of grout. Adhesive at 95 square feet per 50 lb bag with a quarter-inch notch needs 132 ÷ 95 = 1.39, so 2 bags.

Worked example two: the same floor in 12 by 12 inch tile. Each tile now covers one square foot, so 132 square feet means 132 tiles. At twelve tiles a box that is exactly 11 boxes — no rounding waste at all, which is luck rather than planning.

The grout changes more than you would expect. The cell is 12.125² = 147.015625 against a tile of 144, so the fraction rises to 3.015625 ÷ 147.015625 = 0.0205123 — a third more grout per square foot, because smaller tiles mean more linear feet of joint. Over 132 square feet that is 146.21 cubic inches, or 9.98 lb, against 7.51 lb for the larger tile.

Reading the Waste Table and the Grout

Look at the waste table before settling on an allowance, because box rounding often makes the decision for you. On this floor, anything from 10% to 20% buys the same nine boxes — so there is no reason to be stingy. Only the jump down to 5% saves a box, and it leaves almost nothing spare.

Tile size drives grout more than area does. Smaller tiles mean more joints per square foot, and the effect is substantial: 12 by 12 tile needs a third more grout than 12 by 24 over the same floor. Mosaic sheets can need several times as much again, which is why estimating grout by floor area alone goes badly wrong.

The trowel notch is the single biggest lever on adhesive. A quarter-inch square notch covers about 95 square feet per 50 lb bag; a half-inch notch covers 45. Large format tile needs the bigger notch to achieve proper coverage on the back of the tile, so the material cost roughly doubles with the tile size.

Keep more spare tile than you think you need — a full box if you can. Tile is produced in batches with real shade variation, discontinued regularly, and impossible to match years later. Replacing one cracked tile with a visibly different one is a repair everyone can see.

The square footage calculator handles awkward room outlines before you get here, and the flooring calculator covers the same job in laminate or engineered board, where the waste rules are different.

Five Things That Move the Quantity

Five things that move the real quantity.

Layout pattern. A straight grid wastes least. A brick or running-bond offset wastes a little more, a diagonal lay wastes 15% or so, and herringbone with large-format tile can reach 20% because every piece is cut. Pattern matters more than room size.

Room shape. Every alcove, doorway, pillar and pipe means cutting around something, and the offcuts from curved or angled cuts are rarely reusable. A plain rectangle at 10% and a bathroom full of fittings at 10% are not comparable estimates.

Breakage. Tiles break on the saw, in transit and while being handled, and large-format tiles break more easily than small ones. Professional installers routinely allow 10% for cuts and another 5% for breakage on large format.

Substrate flatness. An uneven floor is filled with adhesive, which consumes considerably more than the notch coverage suggests and can double the bag count on a bad slab. Levelling compound first is cheaper than adhesive and produces a better floor.

Grout colour changes the shopping list. Sanded and unsanded grouts are not interchangeable — joints below an eighth of an inch generally need unsanded, wider joints need sanded — and epoxy grout has entirely different coverage and cost. Confirm which type before converting a volume into bags.