Tile Calculator

How Many Tiles an Area Needs

Tile is counted by area, then converted to whole boxes. Work out the area to be covered, divide by the area of one tile, round up, then add a waste allowance based on the layout pattern.

A worked example

A bathroom floor 8 feet by 10 feet is 80 square feet. Using 12 x 24 inch tile, each tile covers 2 square feet, so the neat count is 40 tiles. In a straight lay pattern, add 10 percent, which is 44 tiles. If the tile comes 6 to a box, that is 7.33 boxes, so 8 boxes, or 48 tiles. The extra 4 tiles are not waste, they are the start of a repair stock.

Waste Allowance by Pattern

Waste is not padding, it is the material that goes into cuts. Every tile cut at a wall leaves an offcut that is usually the wrong size for anywhere else, and the more diagonal cuts a pattern needs, the more of each tile ends up in the bucket.

• Straight lay, square or offset: 10 percent. Cuts happen only at the perimeter and around fixtures.
• Diagonal, 45 degrees: 15 percent. Every perimeter tile is a triangle cut, and the offcuts rarely fit the opposite wall.
• Herringbone and chevron: 15 percent, and 20 percent on a small or awkwardly shaped room, because the pattern generates cuts on every edge and the setting out has to be exact.
• Large format, 24 inches or more: 15 percent. A single bad cut or a cracked tile costs a lot more area.
• Mosaic sheets: 10 percent, and count in sheets rather than in individual tiles.

Add to the waste figure, not the other way round, where the room has many angles, a curved edge, a hearth, or many pipe penetrations. Also allow more where the tile is natural stone with heavy variation, because some pieces will be rejected on appearance rather than on fit.

Grout Joints and the Count

A grout joint takes up floor area, so in strict arithmetic wider joints mean fewer tiles. In practice the effect is small. A 12 x 12 inch tile with a 1/16 inch joint occupies 12.0625 inches square, or 1.0105 square feet. With a 1/4 inch joint it occupies 12.25 inches square, or 1.0417 square feet. Over 100 square feet that is the difference between about 99 tiles and about 96, roughly 3 percent, which the waste allowance already absorbs.

Choose the joint width for the tile, not for the count. Rectified tiles, which are mechanically cut to a precise size, can take joints as narrow as 1/16 inch. Pressed tiles with a natural size variation need 1/8 to 3/16 inch so the joint can absorb the difference. Handmade and stone tile often needs 1/4 inch or more. Setting a narrow joint on a tile with size variation produces visibly crooked grout lines and there is no way to correct it afterward.

Joint width also decides the grout. Unsanded grout is for joints up to 1/8 inch, sanded grout for 1/8 inch and wider. Using unsanded grout in a wide joint leads to shrinkage cracking.

Boxes and Dye Lots

Tile is sold by the box, and boxes are not sold by the piece. A box carries a stated square foot coverage, commonly 10 to 25 square feet depending on tile size, and that figure is what the count should be divided by. Always round up to whole boxes.

Every box carries a dye lot or shade and caliber number. Tile color is fired, and two production runs of the same product will differ enough to be visible across a floor. Buy the entire job from a single dye lot, check the numbers on every box before the installer opens them, and mix tiles from several boxes as the floor goes down so that any within lot variation is spread evenly rather than appearing as a block of darker tile in one corner.

Buy one extra box beyond the calculated need and store it. Discontinued lines and changed dye lots make an exact match impossible later, and a single cracked tile in the middle of a floor is a much bigger problem than one spare box in the garage. Store it flat, dry and labeled with the room and the dye lot number.

Layout Planning

Where the first tile goes decides how the floor looks. Setting out from a wall guarantees a full tile on one side and whatever is left over on the other, and rooms are rarely square, so that leftover strip usually tapers.

Work from the center instead. Snap two chalk lines through the middle of the room at right angles, dry lay a row in each direction, and see what the edge cuts come out at. If a cut lands narrower than about half a tile, shift the whole grid by half a tile so the cuts at both ends are equal and reasonably wide. Slivers along a wall look like a mistake and are hard to cut and to hold.

Then decide which edge matters. In a bathroom, the visual reference is often the tub or the vanity rather than the room center. On a wall, the top course under a ceiling or a cabinet is the one people see, so drop the cut course to the floor where the base or the tub covers part of it. Check the room for square with a 3, 4, 5 triangle before committing, and check the floor for flatness, since large format tile needs a substrate within about 1/8 inch over 10 feet.

Tiles per 100 Square Feet

Figures ignore the grout joint, which changes the count by about 3 percent at most and is absorbed by the waste allowance. Divide the final tile count by the pieces per box, then round up to whole boxes.

Thinset and Grout

Thinset coverage depends on the trowel, not on the tile alone. A 1/4 x 1/4 inch square notch covers roughly 90 to 100 square feet per 50 pound bag, a 1/4 x 3/8 inch notch about 60 to 70, and a 1/2 x 1/2 inch notch used under large format tile about 40 to 45. Large format tile also usually needs back buttering, which cuts coverage further. Grout coverage varies with tile size and joint width, so use the chart printed on the bag rather than a single rule.