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Formula
Tiles = ⌈Area × (1 + Waste ÷ 100) ÷ ((L + g) × (W + g))⌉; Boxes = ⌈Tiles ÷ Tiles per box⌉
- Area
- floor or wall area to be tiled
- L, W
- tile length and width
- g
- grout joint width
- Waste
- extra tiles in percent for cuts, breakage and spares (default 10%)
What this tile calculator does
Tile is sold by the box but laid one piece at a time, with a grout joint between each. This tile calculator converts the area you’re covering into a tile count that accounts for the joint width, adds an allowance for cuts and breakage, and rounds up to whole boxes. It works for floors, shower walls, backsplashes and any flat surface, in imperial or metric units.
How to use it
- Area to tile: in square feet, square yards or square meters. For a floor, multiply length × width. For an irregular room, add up the parts with the square footage calculator first.
- Tile length and width: the nominal size on the box, in inches, centimeters or millimeters.
- Grout joint width: optional. 1/8 in is 0.125 and 1/16 in is 0.0625. Leave it empty for no joint.
- Waste allowance: 10% by default.
- Tiles per box and price per box: optional, to get the number of boxes and the cost.
How to calculate tiles by hand
Take a 90 ft² bathroom floor in 18 × 18 in porcelain with 3/16 in (0.1875 in) joints.
- Tile plus joint: 18 + 0.1875 = 18.1875 in on each side.
- Footprint of one tile: 18.1875 × 18.1875 = 330.79 in². Divide by 144 to get square feet: 2.297 ft².
- Tiles before waste: 90 ÷ 2.297 = 39.18
- With 10% waste: 39.18 × 1.10 = 43.1, so 44 tiles.
- At 5 tiles per box: 44 ÷ 5 = 8.8, so 9 boxes, which leaves 1 extra tile.
For rectangular tiles the same steps apply: a 12 × 24 in tile with a 1/8 in joint has a footprint of 12.125 × 24.125 = 292.5 in², or 2.03 ft².
Tiles needed per 100 square feet
Calculated with the tile calculator, using 1/16 in joints for small tiles (under 6 in) and 1/8 in for larger ones.
| Tile size | Joint | Tiles, no waste | Tiles with 10% waste |
|---|---|---|---|
| 3 × 6 in (subway) | 1/16 in | 776 | 854 |
| 4 × 4 in | 1/16 in | 873 | 960 |
| 6 × 6 in | 1/8 in | 384 | 423 |
| 6 × 36 in (plank) | 1/8 in | 66 | 72 |
| 12 × 12 in | 1/8 in | 98 | 108 |
| 12 × 24 in | 1/8 in | 50 | 55 |
| 18 × 18 in | 1/8 in | 44 | 49 |
| 24 × 24 in | 1/8 in | 25 | 28 |
Choosing a waste allowance
Daltile recommends buying about 10% more tile than you expect to need. That covers cut pieces at the walls, a few breakages and some spare tiles, often called attic stock, for future repairs from the same production lot. Adjust it for your job:
- 5–10%: large, simple rooms in a straight grid.
- 10–15%: small bathrooms, rooms with many corners, or running-bond (brick) layouts.
- 15–20%: diagonal and herringbone patterns, natural stone with color variation, or large-format tiles that are expensive to miscut.
Because tile lots vary in shade, buying a little extra now is cheaper than trying to match it later.
Real-world tips
- Measure each surface separately. Floor, shower walls and backsplash often use different tiles, so run each through the tile calculator on its own.
- Subtract fixed items. Don’t tile under a bathtub, vanity base or kitchen island unless you plan to.
- Check the actual size. A “12 × 24” tile can be 11.8 × 23.6 in. Use the size printed on the box when the difference matters.
- Round to full boxes, and keep the spares. Unopened boxes can often be returned, while a missing box from the same lot can be hard to replace.
Common mistakes
- Mixing up square inches and square feet. A 12 × 12 in tile is 144 in², which is 1 ft². Divide square inches by 144.
- Ignoring the joint on small tiles. On 4 × 4 in tiles with 1/16 in joints, the joints change the count by about 3%.
- Applying waste to boxes instead of tiles. Add the allowance before you divide into boxes, or rounding can leave you short.
- Using one waste figure for every layout. A diagonal layout wastes far more at the edges than a straight one.
Other estimates for the same room
For wood, laminate or vinyl plank floors sold by coverage per box, the flooring calculator is the better fit. If you’re painting the walls above the tile, the paint calculator works out the gallons.
Glossary
- Grout joint: the gap between tiles filled with grout, usually 1/16 to 1/4 in.
- Nominal size: the size a tile is sold as, which can differ slightly from its actual size.
- Attic stock: spare tiles kept after installation for future repairs.
- Large-format tile: tile with at least one side 15 in or longer.
Worked examples
A bathroom floor in 12 × 12 tiles
64 ft² of floor, 12 × 12 in tiles with 1/8 in joints, 10% waste, 15 tiles per box.
Inputs: Area to tile = 64; Area to tile unit = Square feet; Tile length = 12; Tile length unit = Inches; Tile width = 12; Tile width unit = Inches; Grout joint width = 0.125; Grout joint width unit = Inches; Waste allowance = 10 %; Tiles per box (optional) = 15
Tile footprint: (12 + 0.125) × (12 + 0.125) = 147.02 in² Tiles: 64 ft² ÷ 1.0209 ft² = 62.69 With waste: 62.69 × 1.1 = 68.96 → 69 tiles Boxes: 69 ÷ 15 = 4.6 → 5
Answer: 64 ft² with 12 × 12 in tiles and 10% waste needs 69 tiles (5 boxes).
A kitchen in large-format 12 × 24 porcelain
185 ft² of kitchen floor, 12 × 24 in tiles with 1/16 in joints, 10% waste, 8 tiles per box at $52 a box.
Inputs: Area to tile = 185; Area to tile unit = Square feet; Tile length = 24; Tile length unit = Inches; Tile width = 12; Tile width unit = Inches; Grout joint width = 0.0625; Grout joint width unit = Inches; Waste allowance = 10 %; Tiles per box (optional) = 8; Price per box (optional) = $52
Tile footprint: (24 + 0.063) × (12 + 0.063) = 290.25 in² Tiles: 185 ft² ÷ 2.0157 ft² = 91.78 With waste: 91.78 × 1.1 = 100.96 → 101 tiles Boxes: 101 ÷ 8 = 12.63 → 13
Answer: 185 ft² with 24 × 12 in tiles and 10% waste needs 101 tiles (13 boxes).
A metric backsplash in subway tile
3.2 m² of wall, 20 × 10 cm subway tiles with 2 mm joints, 15% waste for the many cuts around outlets.
Inputs: Area to tile = 3.2; Area to tile unit = Square meters; Tile length = 20; Tile length unit = Centimeters; Tile width = 10; Tile width unit = Centimeters; Grout joint width = 2; Grout joint width unit = Millimeters; Waste allowance = 15 %
Tile footprint: (20 + 0.2) × (10 + 0.2) = 206.04 cm² Tiles: 3.2 m² ÷ 0.0206 m² = 155.31 With waste: 155.31 × 1.15 = 178.61 → 179 tiles
Answer: 3.2 m² with 20 × 10 cm tiles and 15% waste needs 179 tiles.
Exact fit with no grout or waste (edge case)
100 ft² covered by 6 × 6 in tiles with no joint and no waste: exactly 400 tiles, with no float rounding up to 401.
Inputs: Area to tile = 100; Area to tile unit = Square feet; Tile length = 6; Tile length unit = Inches; Tile width = 6; Tile width unit = Inches; Waste allowance = 0 %
Tile footprint: (6 + 0) × (6 + 0) = 36 in² Tiles: 100 ft² ÷ 0.25 ft² = 400 With waste: 400 × 1 = 400 → 400 tiles
Answer: 100 ft² with 6 × 6 in tiles and 0% waste needs 400 tiles.
Assumptions and limitations
- This is an estimate only, not professional installation or engineering advice. The real count depends on the room's shape, the layout and where cuts fall.
- Each tile is counted as occupying its own face plus one grout joint along two edges, (L + g) × (W + g), which is how a laid grid repeats.
- The waste allowance defaults to 10% if left empty, in line with Daltile's recommendation to buy about 10% more tile than you expect to need. Use 15% or more for diagonal or herringbone layouts, small rooms with many cuts, or natural stone.
- Tiles and boxes are rounded up to whole numbers. Partial tiles from cuts are not reused.
- US units are the default (square feet and inches). Choose square meters and centimeters or millimeters to work in metric.
- Grout, thinset, trim pieces and bullnose edges are not included.
Frequently asked questions
How do I calculate how many tiles I need?
Divide the area by the area of one tile, then add your waste allowance and round up. For 12 × 12 in tiles (1 ft² each), a 150 ft² floor needs 150 tiles, or 165 with 10% extra. Grout joints make each tile cover slightly more, so the count drops a little.
How much extra tile should I buy?
Daltile recommends about 10% more than the area you're covering. Use 15% for diagonal or herringbone patterns and rooms with lots of corners, and keep a few spare tiles from the same lot for future repairs.
How many 12x24 tiles are in a box?
It varies by product and thickness, so check the label. Boxes of large-format porcelain often hold 6–8 tiles, about 12–16 ft². Enter the count from your box to get the number of boxes.
Does grout width change the number of tiles?
Slightly. Each tile plus its joint covers more area than the tile alone. With 12 × 12 in tiles and 1/8 in joints, 100 ft² needs 98 tiles instead of 100. With small mosaics, wide joints make a larger difference.
How many tiles do I need for 100 square feet?
With 1/8 in joints and no waste, about 98 tiles of 12 × 12 in, 50 of 12 × 24 in, 44 of 18 × 18 in or 25 of 24 × 24 in. Add 10% for cuts and breakage.
Can I use this for a backsplash or shower wall?
Yes. Enter the wall area, measured as width × height, minus windows, outlets you won't tile around, and cabinets. Small tiles on walls usually need more waste because of the many cuts around fixtures.
Sources
- Tile & Natural Stone FAQs — Daltile. Checked October 12, 2026.
- NIST Guide to the SI, Appendix B.9: Factors for units listed by kind of quantity — National Institute of Standards and Technology. Checked October 12, 2026.