Tile Calculator

Background.

The question usually arrives as one measurement and a tile already chosen: a 120-square-foot bathroom floor and a 12 × 24 inch porcelain, say. Each of those tiles covers 2 square feet, so 60 tiles would cover the floor on paper. That is not the number to carry to the checkout. Tiles along the walls get cut and their offcuts rarely fit anywhere else, a few crack under the cutter or arrive chipped, and the store sells the product in sealed cartons rather than by the piece. What you get here is the shopping quantity: whole tiles, a waste allowance on top of them, then whole boxes and what they cost.

Grout is counted as well. Each tile is treated as claiming its own face plus one joint along a long edge and one along a short edge, so a 12 × 24 tile laid with 1/8-inch joints occupies 12.125 by 24.125 inches. For a tile that size the joint adds only about 1.6% to its footprint. Around a 4-inch square the same joint adds more than 6%, which on 60 square feet of small tile takes more than 30 pieces off the order.

The waste percentage is a judgement about the layout. Ten percent is the usual starting allowance for a straight grid in a plain rectangular room; diagonal and herringbone patterns, rooms full of corners and pipes, and long tiles that have to be staggered all call for more. Because the count is then rounded up to whole cartons, part of any allowance is often absorbed by the box you were going to buy anyway.

There is a second reason not to cut the order fine. Tile is fired in production runs, and cartons carry shade and caliber codes because one run can differ from the next in colour and very slightly in size. Going back for one more box after the floor is half laid risks a carton that does not match, and leftover tiles from the original lot are the only repair stock you can rely on when a tile cracks years later.

The method fits any flat surface covered with a single tile size: floors, walls, backsplashes, shower surrounds. It does not draw the layout, so it cannot say where the cut rows will fall, and it leaves out trim pieces, thinset, grout and backer board.

What is tile calculator?

A tile estimate is really three counts stacked on one another. The raw count is how many grout-adjusted tile footprints fit into the area, rounded up, because a fraction of a tile still has to be a whole tile. The tiles-to-buy count adds the waste allowance to that figure and rounds up again. The box count divides by the number of pieces in a carton and rounds up a third time, since no store will split a box. Each step can only add tiles, so the cartons you pay for always hold at least the waste-adjusted count and usually a few more. The module area, in square feet, is reported alongside: it is what one tile plus its share of the grout lines covers, and dividing your area by it is where the whole estimate starts.

How to use this calculator.

1. 01Enter the Project area in square feet. Measure length and width in feet and multiply; split an L-shaped room into rectangles and add them; for wall tile, subtract windows and doors. If your plan is in square metres, multiply by 10.764.
2. 02Enter Tile length and Tile width in inches from the product specification rather than the name on the label. A tile sold as 12 × 24 may be a metric 300 × 600 mm piece, which measures 11.81 × 23.62 inches; divide millimetres by 25.4 to get inches.
3. 03Set Grout joint width to the spacer you plan to use: 0.0625 for 1/16 inch, 0.125 for 1/8 inch, 0.1875 for 3/16 inch. The manufacturer's installation information gives the narrowest joint that tile allows.
4. 04Choose a Waste allowance. Start around 10% for a straight grid in a simple room and go higher for diagonal or herringbone layouts, many cuts around obstacles, or your first job with a tile cutter.
5. 05Enter Tiles per box from the carton. If the carton lists only square feet, divide that by the area of one tile (length × width ÷ 144); for tile sold individually, enter 1.
6. 06Add Price per box if you want a cost, or the price of one tile if you entered 1 per box. Then order the Box count, and check that every carton carries the same shade and lot code before any are opened.

The formula.

The estimate runs in four steps. First the module area: M = (L + g) × (W + g) ÷ 144, where L and W are the tile's length and width and g the grout joint, all in inches. Dividing by 144 converts square inches to square feet, since a square foot is 12 by 12 inches. Adding one joint to each dimension reflects how a grid repeats: every tile brings one joint along a long side and one along a short side, and the next tile starts where that joint ends.

Second, the raw count R = ⌈A ÷ M⌉, where A is the project area and the brackets mean round up to the next whole number. Third, the purchase count T = ⌈R × (1 + w)⌉, with w the waste allowance as a fraction (10% is 0.10). The allowance is applied to the already rounded raw count, so 10% of 60 tiles is exactly 6 more. Fourth, boxes B = ⌈T ÷ n⌉ for n tiles per carton, and cost C = B × p for a box price p. The box step carries its own hidden overage of anywhere from zero to n − 1 tiles.

Two assumptions sit inside the module. It describes a uniform grid where tiles and joints alternate across the whole surface, and it counts no offcuts: the cut pieces at the perimeter are paid for entirely by the waste allowance. It also assumes one tile size, so a pattern that mixes sizes needs each size run separately on its own share of the area.

How much each input moves the answer depends on the tile. On 60 square feet of 4-inch square tile, widening the joint from 1/8 to 3/16 inch lowers the raw count from 508 to 493, while raising the waste allowance from 10% to 15% lifts the purchase from 559 tiles to 585. On a 120-square-foot floor of 12 × 24 tile, the 1/8-inch joint changes nothing at all: the raw count is 60 with or without it.

A worked example.

Frequently asked questions.

References& sources.

1. [1]Tile Council of North America (2025). "TCNA Handbook for Ceramic, Glass, and Stone Tile Installation." TCNA.
2. [2]American National Standards Institute (2024). "ANSI A108/A118/A136: American National Standard Specifications for the Installation of Ceramic Tile." ANSI Webstore.
3. [3]Tile Council of North America (2025). "Grout: Frequently Asked Questions." TCNA.
4. [4]National Institute of Standards and Technology (2026). "NIST Handbook 133, Appendix E: General Tables of Units of Measurement." U.S. Department of Commerce.
5. [5]Bureau International des Poids et Mesures (2019). "The International System of Units (SI Brochure), 9th edition." BIPM.