Tile Calculator

How to use this calculator

1. Measure the area. For a simple room, enter the length and width in feet. For anything else, switch to Square feet and enter the total you worked out.
2. Pick the tile size from the list. Inch sizes are nominal. If the box gives a metric size, pick the matching mm size, or choose Custom size and enter the actual size.
3. Choose the grout joint and layout. Each layout fills in a rule-of-thumb waste percentage, which you can change.
4. Add the box coverage (optional). Type the square feet per box, or tiles per box, from the box label to get the number of boxes and the real cost. If you want an unopened box for future repairs on top of the waste allowance, choose Add 1 box under Spare box.
5. Open Price & setting materials to set your tile price, trowel and tile thickness. These drive the cost, thinset and grout estimates.

How to measure for tile

• Rectangular rooms: measure wall to wall at the widest points. Measure to the wall, not the baseboard, because the tile runs under the baseboard edge.
• L-shaped and odd rooms: split the floor into rectangles, multiply length × width for each and add them up. Include closets and the area under a freestanding tub or vanity if the tile goes there.
• Walls and showers: measure each wall separately (width × height up to where the tile stops) and add them together. Subtract windows and doors only if they are large. Measure the shower floor on its own, since it usually takes a smaller mosaic tile.
• Use the actual tile size. Tile is sold by a rounded (nominal) size. If the box or spec sheet lists the real size, use that. For example, 300 × 300 mm tile is 11.81 in, and with a 1/8 in joint it takes about 3% more tiles than a true 12 in tile (122 instead of 118 for 120 sq ft). If you have a sample, measure it and enter it as a custom size.

The formula

Each tile covers its own area plus half a grout joint on every side, so the math uses that “tile + joint” size:

Area per tile (sq ft) = (tile width + joint) × (tile length + joint) ÷ 144 (all in inches)

Tiles = area to tile ÷ area per tile × (1 + waste %), rounded up

Square feet to order is the number of tiles times the face area of one tile. Box labels count face area, so compare that figure with the box. Boxes are always rounded up.

The joint matters more than you might expect. A 1/4 in joint on a 3 × 6 in subway tile takes up about 11% of the wall, so leaving it out would have you buying too much tile.

Worked example: a 12 × 10 ft bathroom floor

12 × 12 in porcelain tile, 1/8 in joints, straight layout:

• Area: 12 × 10 = 120 sq ft
• Area per tile: 12.125 × 12.125 ÷ 144 = 1.021 sq ft
• Tiles: 120 ÷ 1.021 = 117.5 → with 10% waste, 129.3 → 130 tiles
• Boxes at 15 sq ft per box: 130 ÷ 15 = 8.7 → 9 boxes (135 sq ft, $405 at $3 per sq ft)
• With a spare box for repairs: 10 boxes (150 sq ft, $450)
• Thinset with a 1/4 × 3/8 in notch (60 sq ft per bag): 120 ÷ 60 = 2 × 50 lb bags
• Sanded grout: about 8.5 lb, so one 25 lb bag (the Polyblend Plus chart gives 120 ÷ 348 × 25 = 8.6 lb)

How much extra tile to buy for each layout

Waste comes from the tiles you cut at walls, doors and corners, plus a few that break or have defects. Layouts with more cuts at the edges need more extra tile. No ANSI or TCNA standard sets an overage, so the calculator’s defaults are rules of thumb:

Artistic Tile also recommends at least 30% for tile 18 × 36 in and larger. Its higher figures make sense for natural stone, mosaics and costly tile you can’t easily reorder. For a simple room with plain porcelain, the lower rule of thumb is a reasonable start. For small rooms with lots of corners, go higher.

Shade variation and a spare box

Tile varies in shade. The TCNA Handbook and ANSI A137.1 grade it from V0 (very uniform) to V4 (substantial, random variation). The Ceramic Tile Education Foundation advises looking at several pieces, not one sample, and making a mock-up before the job. Also, if the boxes show a lot or shade code, check that they all match before you open them.

Cuts and breakage use up the waste allowance, so it won’t leave you a box for later. For an unopened repair box, use the Spare box option. It is added after the waste and rounding, and it is included in the cost.

Thinset and grout

Thinset coverage depends on the trowel notch. The calculator uses the lower figure of each range in Custom Building Products’ VersaBond Professional Tile Mortar data sheet (TDS-119, published October 7, 2026), which gives the most bags:

The Auto pick is a rule of thumb, since no standard ties notch size to tile size. The data sheet says larger tiles, tiles with deep back patterns and ungauged stone may need a bigger notch and back troweling (back-buttering). These figures cover the trowelled bed only. Back-buttering is not included. Estimate it from the tile’s back pattern and add it, as the data sheet says. The same sheet requires mortar to cover at least 80% of the tile back in dry areas and 95% in wet areas and outdoors, so pull up a tile now and then to check.

Grout fills the joints, so the amount depends on the joint width, the tile size and the tile thickness, which sets the joint depth. The calculator works out the joint volume per square foot and converts it to pounds with a factor taken from the Polyblend Plus coverage charts. Against the 25 lb sanded and 10 lb non-sanded charts, the result compares like this:

• Tile 4 in and larger: within 3% of every chart value, both in pounds and as coverage per bag.
• 3 × 3 in tile: from 0.3% less to 5.1% more grout. As coverage per bag, that is from 4.9% less to 0.3% more.
• 1 and 2 in mosaics: more grout than the chart, up to about 23% more for 1 in tile with a 1/2 in joint.

The chart is an estimate too. Custom Building Products notes that coverage may vary with installation practices and jobsite conditions, so neither figure is a guaranteed maximum.

Backer board in showers and around tubs

Behind wall tile in tub and shower areas, the 2024 IRC (R702.4.2) allows only the backer materials in its Table R702.4.2:

• glass-mat gypsum backing panel (ASTM C1178)
• fiber-reinforced gypsum panels (ASTM C1278)
• non-asbestos fiber-cement backer board (ASTM C1288 or ISO 8336, Category C)
• fiber-mat-reinforced cementitious backer units (ASTM C1325)

Install them to the manufacturer’s recommendations. The calculator doesn’t count backer board, so measure the wall area for it separately.

Tips before you buy

• Tile 15 in or longer needs a flatter floor. For tile with at least one edge of 15 in or more, ANSI A108.02 allows the floor to vary by no more than 1/8 in in 10 ft, and 1/16 in in 24 in measured from the high points. Check with a straightedge and plan for leveler where it is out. Strictly, ANSI A108.T defines “large format” as tile with a side over 23 in, but these limits start at 15 in.
• Limit the offset on long tile. For brick and other offset layouts where the offset side is over 15 in (nominal), ANSI A108.02 sets a maximum offset of 33% unless the tile manufacturer specifies otherwise. If a larger offset is specified, the specifier and the owner must approve the mock-up and the lippage (uneven edges between tiles). The calculator’s brick drawing switches to a 33% offset for these tiles (7.92 in on a 24 in tile).
• Use a wide enough joint in running bond. For brick layouts with any side over 15 in, ANSI A108.02 calls for an average joint of at least 1/8 in for rectified tile or 3/16 in for calibrated tile, plus the tile’s edge warpage. A 1/16 in joint doesn’t qualify. The calculator warns you but still counts the tile.
• Check the current ANSI edition. These limits were checked against A108.02-2023 and A108.T-2023, as quoted by the Ceramic Tile Education Foundation, Stone World and NTCA’s TileLetter. The current compilation is ANSI A108-A118-A136.1, American National Specifications for the Installation of Ceramic Tile - July 2026 (TCNA). TCNA’s standards status page still lists A108.02 and A108.T as 2023 editions, but we have not read the July 2026 text, and TCNA notes that A108.T is open for possible revisions. Confirm against the current edition before you rely on these limits for a specification.
• Lay it out dry first. A common practice is to start from the center lines of the room, so cut tiles at opposite walls are the same width, and to avoid slivers under about half a tile.
• Don’t forget trim. Bullnose, edge profiles and transition strips are sold separately. Count them by the linear foot.

Last reviewed Oct 9, 2026. See how we calculate. Results are planning estimates - confirm with your supplier and local code.