Tile Calculator

Each tile covers width × height ÷ 144 square feet, because 144 square inches make a square foot. A 12 by 12 in tile is therefore exactly 1 sq ft, an 18 by 18 in tile is 2.25 sq ft, and a 6 by 24 in plank is 1 sq ft as well. Divide the area plus overage by the tile area and round up: 120 sq ft with 10% overage and 1 sq ft tiles needs 132 tiles. Boxes are the tile count divided by the tiles per box, rounded up again. Two things to watch when you enter the tile size. Nominal size is not actual size — a tile sold as 12 by 12 in often measures a little under, and the grout joint makes up the difference. And the size on the box is the tile alone; the joint is what turns the tile into a repeating module, which is why a wall of small mosaic tiles covers more area than the sum of the tiles. Measure the actual space rather than trusting a room label. Tile goes under the toe kick line but not under the tub, into the closet but not into the doorway threshold — walk the perimeter with a tape.

Overage on a tile job is consumed material, not spare inventory. Cuts are the biggest share. Every edge of the field, every doorway, every corner, and every penetration for a toilet flange, drain or pipe means a tile is cut and the offcut is usually unusable. A cut that leaves a sliver has no home anywhere else in the room. Breakage is real and unavoidable. Tiles crack in shipping, snap wrong at the score line, and chip at the edge on the wet saw. Large-format and thin porcelain break more easily than small tile. Future repair is the reason to keep the last box. Tile survives decades, and a product bought today will not be on the shelf when a chair leg cracks one in five years. A single replacement tile from the original batch is the difference between an invisible repair and re-tiling a room. Ordering the exact square footage guarantees a second trip in the middle of the job, and a second trip guarantees a batch question.

Common practice is around 10% for a straight, grid layout in a simple rectangular room. Installers commonly move to 15% or more for a diagonal layout and higher again for herringbone, chevron or any pattern where pieces meet at an angle. The reason is geometry rather than a rule of thumb. In a straight layout only the two runout walls generate cuts, and the cut tile from one end of a row sometimes starts the next. Rotate the grid 45 degrees and every one of the four walls produces triangular offcuts, none of which fit anywhere else. Tile size compounds it. With large-format tile, one bad cut discards a full square foot or more of material, so a small room in large tile can waste a surprising share of the order. Small tile and mosaic sheets waste less per cut but consume more grout. Rooms with a lot of interruptions — an island, a peninsula, a curbed shower, several doorways — sit at the high end of any range. If you have a layout drawing, count the cut tiles directly instead of applying a percentage; that is what a tile setter does.

Ceramic and porcelain get their color from glazes and body pigments fired in batches, and a batch is called a dye lot or shade lot. The lot number is printed on the box. Color, gloss and even the exact dimensions can drift slightly from one production run to the next. So buy the whole job, including the overage, at one time and check that the boxes carry the same lot number. Boxes bought weeks apart may not, and a shade difference that is invisible under store lighting can be plain across a finished floor. Separately, many tiles carry a shade variation rating on the box, describing how much the tiles vary by design — from nearly uniform to deliberately random, as with tiles imitating wood or stone. This is intentional variation, not a defect, and the way to handle it is to dry-lay from several boxes at once and shuffle the tiles before setting any of them. Working straight out of one box at a time concentrates whatever variation exists into visible patches.

The tile count is the headline number, but the job needs more. Underneath goes thinset mortar, sized by the trowel notch and the tile size; in the joints goes grout, sanded or unsanded depending on joint width. Add spacers, edge trim or bullnose for exposed edges, transition strips at doorways, and sealer if the grout or the stone requires it. The substrate matters more than any of it. Tile needs a flat, rigid, appropriate base — cement backer board or an uncoupling membrane rather than bare drywall in wet areas, and a proper waterproofing layer in showers. Tile and grout are not themselves waterproof; the assembly behind them is what keeps water out, and moisture that gets past it causes mold problems that are invisible until they are expensive. One safety note on the cutting. Dry-cutting ceramic, porcelain and stone releases respirable crystalline silica, which is a recognized lung hazard. Wet-cut, cut outdoors where you can, and use appropriate respiratory protection. This is worth taking seriously even on a one-weekend bathroom.