Tile calculator
Enter the floor or wall size and your tile size to get the number of tiles and boxes, with a waste allowance. The grout estimate is optional. The defaults are a 5 × 8 ft bathroom floor in 12 × 12 in tile.
How the calculator works
- Area = length × width, minus anything you leave out. Most installers don't tile under a vanity cabinet or a tub.
- Tiles = area × (1 + waste %) ÷ the area of one tile, rounded up. The tile's face size is used, not including the joint. That over-counts very slightly, which is the safe direction.
- Boxes = tiles ÷ tiles per box, rounded up.
- Grout is the volume of the joints, then converted to weight. Joint volume per square foot is
(L + W) ÷ ((L + J) × (W + J)) × J × D × 144, in inches. L and W are the tile size, J is the joint width and D is the joint depth, which is roughly the tile thickness.
How the grout estimate was checked
Grout is sold by weight, so the calculator needs a density. It uses one constant: a 25 lb bag of sanded grout fills about 384 in³ of joint. That figure was back-calculated from CUSTOM Building Products' published coverage chart for Polyblend Sanded Grout. The test suite checks the calculator against nine rows of that chart, from 1 × 1 in mosaics to 24 × 24 in tile, and every row comes out within 3%. For example, 12 × 12 × 3/8 in tile with 1/8 in joints covers 348 ft² per 25 lb bag. Unsanded, epoxy and other brands' grouts weigh differently. For those, use the maker's chart.
Worked example: a 5 × 8 ft bathroom
- Area: 5 × 8 = 40 ft² (nothing left out)
- Tiles: 40 × 1.10 = 44 ft². Each 12 × 12 in tile is 1 ft², so 44 tiles.
- Grout, 1/8 in joints, 3/8 in tile: about 2.9 lb, or 3.2 lb with 10% extra. That's one bag, and a small one would do.
Assumptions and things that change the answer
- Waste: 10% for a straight grid and 15% for a diagonal layout are common planning allowances, not a standard. Small rooms with a toilet, a floor drain or a lot of cuts can need more, and so can large-format tile. If your tile maker gives a figure, use theirs.
- Buy from one lot. Shade and size can vary between production runs. Buy everything at once and keep a spare box for repairs.
- Joint size follows the tile, not taste. Very straight rectified tile can take narrow joints. Handmade or cushion-edge tile needs wider ones, which uses more grout.
Cutting ceramic, porcelain or stone tile with a saw or grinder makes respirable crystalline silica dust. OSHA's construction silica rule calls for water at the blade or dust collection. A wet tile saw does this. Cut outside or with good ventilation and wear eye protection. Grout and thinset contain Portland cement, so wear gloves.
Sources
- CUSTOM Building Products, Polyblend Plus Sanded Grout coverage chart, and the Polyblend Sanded Grout data sheet (TDS-129).
- LATICRETE, Project estimator (“Add 10% for waste, spillage and clean-up”).
- OSHA, Respirable crystalline silica in construction (29 CFR 1926.1153).