Tile Calculator

How the tile count works

Each tile brings one joint along its length and one along its width, so the pattern repeats every tile plus one joint. That is why a 12 × 24 in tile with a 1/8 in joint covers 2.03 sq ft, not 2. The joint matters more for small tiles: 100 sq ft of 3 × 6 in subway tile with 1/16 in joints takes 776 tiles, not the 800 you get by dividing by the tile alone.

The calculator works from the size you enter. Tiles are named by a nominal size and are often a little smaller: Emser’s “12 × 24” Potenza is 11.73 in wide.^[1] If the spec sheet lists the actual size, enter that, and count boxes from the sq ft printed on the box (below).

Measuring the floor or wall

1. Break the room into rectangles and add each as an area: an L-shaped room is two, and a closet that gets the same tile is one more. Round each measurement up to the next inch. The square footage calculator has more shapes.
2. Subtract what you will not tile, such as a tub or a kitchen island that sits on the subfloor: add it as an area and tick “Subtract this area”.
3. For walls and backsplashes, measure only the tiled part, width times height, and set “Where” to wall. A tub surround is three walls added together.

Example: a kitchen floor in 12 × 24 in tile

The kitchen is 14 × 12 ft with a 6 × 3 ft island that stays on the subfloor. The tile is 12 × 24 in pressed porcelain (Florida Tile’s Urban Foundry, for example^[2]), so its joints are 3/16 in, the minimum for pressed tile over 15 in (see joint width below). It is laid in a straight grid, and the carton says 15.30 sq ft.

1. Area: 14 × 12 − 6 × 3 = 150.00 sq ft
2. Extra for a straight grid, 10%: 150.00 × 1.10 = 165.00 sq ft
3. One tile with its joint: (24 + 0.1875) × (12 + 0.1875) ÷ 144 = 2.0471 sq ft
4. Tiles: 165.00 ÷ 2.0471 = 80.60 → 81 tiles
5. Boxes: 165.00 ÷ 15.30 = 10.78 → 11 boxes
6. Grout: about 12.1 lb with 10% extra, so one 25 lb bag (the grout calculator has brand presets)
7. Thin-set: the long side is 24 in, so a 1/2 × 1/2 in square notch trowel at about 40 sq ft per 50 lb bag: 150.00 ÷ 40 = 3.75 → 4 bags

Example: a subway tile backsplash

The backsplash runs 10 ft along the counter and 18 in up to the cabinets. The tile is 3 × 6 in subway, 1/4 in thick, with 1/16 in joints in a running bond (each row shifted half a tile).

1. Area: 10 × 1.5 = 15.00 sq ft; with 15% extra for an offset layout, 17.25 sq ft
2. One tile with its joint: (6 + 0.0625) × (3 + 0.0625) ÷ 144 = 0.1289 sq ft
3. Tiles: 17.25 ÷ 0.1289 = 133.79 → 134 tiles
4. Grout: the joint is under 1/8 in, so unsanded; about 1.1 lb, one 10 lb bag
5. Thin-set: 6 in wall tile takes a 3/16 × 5/32 in V-notch trowel, and 15.00 sq ft is a fraction of one 50 lb bag (about 150 sq ft)

How much extra tile to buy

Extra covers cuts at walls and doorways, tiles that break, and spares for later repairs. We found no figure from a tile standards body; these are recommendations from tile makers, tile sellers and home-improvement writers, and they vary a lot. Shipping breakage (Clé 2–4%, Bob Vila 2–3% of boxed tiles^[3][4]) is treated as part of the figures, not added on top.

The straight-lay 10% is the smallest figure on which MSI, Clé’s article and Bob Vila agree; Clé’s own calculator starts at 15%, so 10% is the lean end of the range. We found no published number for a plain running bond, so the 15% for offset layouts is our estimate, set between the straight grid and the diagonal. Diagonal layouts leave triangles at every wall, and the smaller the room, the larger their share: under 50 sq ft the calculator suggests 25% (our rule of thumb). If your installer gives a figure, type it in the extra field.

Count boxes from the sq ft on the box

Tile is sold in whole boxes, and the number of tiles per box is not standard. MSI packs its 12 × 24 in Dimensions series 8 to a box and its Eramosa series 6.^[10] The coverage printed on the box is usually a little less than the piece count times the nominal size:

For 200 sq ft of 12 × 24 in tile with 10% extra (220.00 sq ft):

• From the piece count: 109 tiles (each counted with its joint) ÷ 8 per box = 13.63 → 14 boxes, counting each tile at its nominal 2 sq ft plus its joint
• From the box: 15.30 sq ft per box, 220.00 ÷ 15.30 = 14.38 → 15 boxes

The piece count leaves you 1 box short. Enter the printed sq ft in “Coverage per box” and use “Tiles per box” only when the box gives nothing else. Buy every box from the same lot so shade and size match.

Grout joint width

Tiles vary slightly in size, and the joint has to absorb it. The installation standard ANSI A108.02, as quoted by the Ceramic Tile Education Foundation, says:^[13]

• A grout joint is never narrower than 1/16 in (4.3.8).
• The joint is at least three times the actual variation in tile size: tiles that vary by 1/16 in need a 3/16 in joint (4.3.8).
• For tile with any side over 15 in, the average joint is at least 1/8 in for rectified tile (edges ground square after firing) and 3/16 in for calibrated tile (4.3.8.1).

Custom Building Products gives the same 1/8 in and 3/16 in minimums as TCNA recommendations and adds the tile’s warpage on top, for example 1/8 in + 1/32 in = 5/32 in.^[14] In practice that means about 3/16 in for pressed porcelain and ceramic and about 1/8 in for rectified tile.^[15] The tile maker’s recommendation comes first: Emser lists 3/16 in for its pressed 12 × 24 in Potenza.^[16]

Joint width barely changes the count (100 sq ft of 12 × 24 in tile takes 49.61 tiles with 1/16 in joints and 48.85 with 3/16 in), but it changes the grout in proportion; see the grout calculator.

Offset layouts with long tiles. For tile over 18 in, TCNA recommends an offset of no more than 33% rather than half a tile, to minimize lippage (uneven edges between tiles), as cited by Custom Building Products.^[14] The calculator reminds you when you pick an offset layout with long tiles.

Tiles per 100 sq ft

Computed by the calculator for 100 sq ft. The joint is 1/8 in (on tile over 15 in, only for rectified tile) except for the 3 × 6 in subway tile at 1/16 in. The 24 × 48 in tile is large format, so its extra includes the +5 points.

For another area, divide the area to order by the “one tile with joint” figure and round up, or let the calculator do it. Herringbone takes the same 20% as diagonal and needs rectangular tiles.

Thin-set mortar: trowel and bags

The trowel’s notch sets how much mortar goes under the tile, and bigger tiles need deeper notches. Custom Building Products lists a V-notch for tile up to 6 × 6 in, a 1/4 × 1/4 in square notch up to 12 × 12 in and 1/4 × 3/8 in up to 16 × 16 in for its pre-mixed SimpleSet,^[17] and MAPEI calls for a 1/2 × 1/2 × 1/2 in square notch on tile over 15 in.^[18] The calculator picks the trowel from the tile’s longer side, with breaks at 6, 12 and 15 in (our choice where the two makers differ).

Square feet per 50 lb bag from each maker’s data sheet.^{[19][20][21][22][23][24][25]} CBP’s sell sheet and product page disagree for the 1/4 × 1/4 in notch, so both are shown. Across the four makers that notch spans 75–106 sq ft per bag; the calculator uses 80, from the low part of the ranges, so you are less likely to run out. If you know your brand, divide by its figure instead. For the V-notch only TEC gives a 50 lb figure; CBP’s SureBond lists 150–170 sq ft per 40 lb bag, which works out to 188–213 per 50 lb.^[26]

• Coverage under the tile. MAPEI and CBP call for at least 80% mortar contact in dry indoor areas and 95% in showers and other wet areas and outdoors; MAPEI cites ANSI A108.5 and TCNA for it.^[23][19] CBP also asks for at least 3/32 in of mortar under the tile once it is pressed in.^[19] Lift a freshly set tile now and then to check.
• Back-buttering (a skim coat on the back of the tile, common with large tiles) is not in these figures, so buy extra if you will do it.
• Lightweight mortar is sold in lighter bags that cover like a standard one: LATICRETE’s 254 Platinum Plus covers 80–95 sq ft per 25 lb bag with a 1/4 × 1/4 in notch, the same as its standard mortar per 50 lb.^[27][22] Count bags by the coverage on the bag, not its weight.
• Over an uncoupling membrane such as Schluter DITRA you need mortar twice: 150–200 sq ft per 50 lb bag to bond the membrane to the floor, and 40–50 sq ft per bag for the tile on top.^[28] The calculator counts only the tile layer.

Related calculators

• Grout calculatorPounds and bags of grout by tile size, joint and brand
• Square footage calculatorAdd up rooms and odd shapes in feet and inches
• Carpet calculatorSquare yards to order from the roll width
• Wallpaper calculatorRolls by wall width, height and pattern repeat
• Project materials listPrint everything you added from each calculator

Prepared by the Yard & Build editors. The formulas behind this calculator are checked against hand-worked answers every time the site is built. Waste figures, joint rules, box coverage and thin-set data sheets checked October 5, 2026.