Divide the area you are tiling by the area of one tile, round up, and then add 10% for cuts — or 15% for a diagonal or herringbone layout. A 10×10 ft floor is 100 sq ft, so it takes 100 tiles of 12×12 in (1 sq ft each), or 110 tiles once you allow 10% waste. The same floor in 12×24 in tiles (2 sq ft each) takes 50 tiles, or 55 with waste. A 12×12 ft room is 144 sq ft: 144 tiles, 159 with waste. Round all of that up to full boxes, and budget one 50 lb bag of thin-set per 60–100 sq ft plus about 11 lb of grout for every 100 sq ft.
The formula, in three steps
- Get the area. Length × width in feet for a floor; height × width for a wall. An L-shaped room is two rectangles added together.
- Divide by one tile. Tile area in square feet = (width in inches × length in inches) ÷ 144. A 12×24 in tile is 288 ÷ 144 = 2 sq ft; an 18×18 in tile is 324 ÷ 144 = 2.25 sq ft.
- Add waste and round up. Tiles to order = your tile count × (1 + waste%). You cannot buy a fraction of a tile, so always round up.
The tile calculator runs those three steps for any format and any room, and the square footage calculator handles the awkward shapes — circles, triangles, L-shaped rooms — that a tape measure alone will not settle.
How many tiles per square foot
| Tile size | Sq ft per tile | Tiles per 100 sq ft | Tiles per 100 sq ft with 10% waste |
|---|---|---|---|
| 3×6 in (subway) | 0.125 | 800 | 880 |
| 4×4 in | 0.11 | 900 | 990 |
| 6×6 in | 0.25 | 400 | 440 |
| 12×12 in | 1.00 | 100 | 110 |
| 12×24 in | 2.00 | 50 | 55 |
| 18×18 in | 2.25 | 45 | 49 |
| 24×24 in | 4.00 | 25 | 28 |
Two things drive the count, and neither is the price of the tile: the size of the tile and the shape of the room. A 12×24 in tile halves the count of a 12×12 in tile, but it also produces longer cuts at the perimeter, so the waste percentage usually climbs at the same time.
How much waste to allow
Waste is not a cushion for carelessness — it pays for the cut tiles at every wall, the corners a blade chips, and the few tiles you keep for a repair in three years.
| Layout or situation | Waste allowance |
|---|---|
| Straight (grid) lay, simple rectangular room | 10% |
| Diagonal (45°) lay | 15% |
| Herringbone or chevron | 15% or more |
| Room with many corners, edges, niches or obstacles | 15% |
| Large-format porcelain | Up to 30% |
Retail guidance and manufacturer guidance agree on the floor of that range: 10% over the calculated total is the standard allowance for straightforward wall and floor work, while diagonal runs and patterns such as herringbone need at least 15%, and large-format porcelain — which cracks more easily before it is set — can justify 30%. Daltile frames the same 10% as attic stock: tile bought now, stored, and used later to replace a broken tile with a match from the same dye lot, because a colour bought in two years will not match the floor you installed today.
Worked example: a 10×10 ft floor
| Step | 12×12 in tile | 12×24 in tile |
|---|---|---|
| Floor area | 100 sq ft | 100 sq ft |
| Sq ft per tile | 1 | 2 |
| Tiles before waste | 100 | 50 |
| Tiles with 10% waste | 110 | 55 |
| Boxes at 15 sq ft per box | 8 | 8 |
Two rules of thumb fall out of that table: a 10×10 ft room needs about 110 tiles of 12×12 in, and doubling the tile size roughly halves the count.
From tiles to boxes
Boxes, not tiles, are the unit you actually buy, and coverage per box varies by product and format — so work from the square feet per box printed on the label instead of counting tiles.
- Multiply the room area by 1 + waste% to get the square footage to order (100 sq ft → 110 sq ft).
- Divide by the coverage per box printed on the label (for example, 110 ÷ 15 = 7.3 boxes).
- Round up (8 boxes) and check the lot numbers match before you leave the store.
Measuring the room so you do not have to reorder
- Measure in inches and convert. 8 ft 5 in × 5 ft 3 in is 101 in × 63 in = 6,363 in² ÷ 144 = 44.2 sq ft. Working in metres? Multiply length × width for square metres, then multiply by 10.764 for square feet.
- Break up irregular spaces. Draw the floor plan, cut it into rectangles, calculate each one and add them. Alcoves, closets and the strip under a fridge still need tile.
- Subtract openings, then add back the reveals. Deduct every door and window, but add the tile that turns into the jamb.
- Kitchen backsplash, the common case: 8 ft of counter run × 18 in high = 12 sq ft. In 3×6 in subway tile (0.125 sq ft each) that is 96 tiles, or 106 with 10% waste.
- Buy one lot. Manufacturers change shade and calibration between runs; a top-up carton from a different lot shows as a patch once it is grouted in.
Thin-set and grout: the other two numbers
Tile is only half the order. Mortar coverage is set by the trowel notch, which is set by tile size, and grout coverage is set by tile size and joint width.
| Material | Coverage | Source |
|---|---|---|
| Thin-set, 1/4 in × 1/4 in notch (tiles under 8 in) | 90–100 sq ft per 50 lb bag | CUSTOM VersaBond chart |
| Thin-set, 1/4 in × 3/8 in notch (tiles 8–15 in) | 60–67 sq ft per 50 lb bag | CUSTOM VersaBond chart |
| Grout, 12×12 in tile, 3/16 in joint | 234 sq ft per 25 lb bag | CUSTOM TDS-360 |
| Grout, 12×12 in tile, 1/4 in joint | 177 sq ft per 25 lb bag | CUSTOM TDS-360 |
| Grout, 12×24 in tile, 3/16 in joint | 310 sq ft per 25 lb bag | CUSTOM TDS-360 |
A 100 sq ft floor of 12×12 in tile therefore needs the 25 lb bag of grout (about 11 lb at a 3/16 in joint) — a 7 lb box only covers roughly 65 sq ft — and two 50 lb bags of thin-set, because the 60–67 sq ft per bag figure leaves you short at 100 sq ft. Mortar must contact at least 80% of the tile back in dry areas and 95% in wet areas and exteriors, so do not stretch a bag by spreading it thinner.
Worked example: a tub-to-ceiling shower surround
A standard 60 in tub alcove, tiled to 7 ft in 12×12 in tile:
| Surface | Area |
|---|---|
| Back wall: 5 ft × 7 ft | 35 sq ft |
| Two end walls: 2.5 ft × 7 ft each (17.5 sq ft each) | 35 sq ft |
| Total | 70 sq ft |
| Tiles before waste | 70 |
| With 15% waste (corners, niche, valve cuts) | 81 |
Wet walls also add site work that eats tile: a niche has four returns and a shelf, and every valve and shower head is a cut that can fail. That is why showers are quoted at 15% rather than 10%.
Quick checklist
- Measure in feet and inches, convert to decimal feet, multiply length × width.
- Split L-shapes into rectangles and add them.
- Divide the area by the sq ft per tile and round up.
- Add 10% straight lay, 15% diagonal, herringbone or corner-heavy rooms, up to 30% for large-format porcelain.
- Convert to boxes using the coverage on the label and round up again.
- Add one 50 lb bag of thin-set per 60–67 sq ft with a 1/4 in × 3/8 in notch (tiles 8–15 in) or per 90–100 sq ft with a 1/4 in × 1/4 in notch (tiles under 8 in), plus roughly 11 lb of grout per 100 sq ft of 12×12 in tile.
- Keep the leftovers. Ten percent of a floor is a set of matching replacement tiles.
If you are painting or patching the same room, the paint calculator and the drywall calculator use the same 10% waste logic for their own materials, and if the tile is going over a new slab, size the pour with the concrete calculator first.