How to use the tile calculator
- Measure the area. For a floor, measure length and width wall to wall. For a wall or backsplash, use width × height. For L-shaped rooms, work out each rectangle with the square footage calculator and enter the total area. Subtract large areas you won't tile, such as a tub or a kitchen island footprint.
- Choose the tile size or enter a custom size in inches (or centimeters). In metric mode the presets use the metric nominal size shown in brackets, so "12 × 24 in (30 × 60 cm)" is calculated as 30 × 60 cm (11.8 × 23.6 in), not 12 × 24 in. The count can differ by a tile or two between the two modes.
- Set the grout joint. Each tile effectively occupies its own size plus one joint, so wider joints mean slightly fewer tiles. This matters most with small tiles.
- Pick a waste allowance for your layout (see below), then enter what the box label says — either square feet per box or tiles per box.
The tile formula
Tiles = area × (1 + waste %) ÷ area of one tile with grout, rounded up
Boxes = tiles ÷ tiles per box, rounded up
(or, from box coverage: tiles × face area of one tile ÷ sq ft per box, rounded up)
Box coverage printed on the carton is the face area of the tiles inside, without grout, so the calculator converts your tile count back to tile face area before dividing by the box coverage.
Worked example: a 10 × 8 ft bathroom floor in 12 × 24 tile
The floor is 10 × 8 = 80 sq ft; with 10% waste, 88 sq ft. A 12 × 24 tile with a 1/8 in joint occupies 12.125 × 24.125 ÷ 144 = 2.031 sq ft, so 88 ÷ 2.031 = 43.3, which rounds up to 44 tiles.
Each tile has a face area of 2 sq ft, so 44 tiles are 88 sq ft of tile. With boxes covering 16 sq ft (8 tiles), 88 ÷ 16 = 5.5, so buy 6 boxes — 96 sq ft, or 48 tiles.
Why the grout joint matters for small tile
A 30 sq ft backsplash in 3 × 6 in subway tile with a 1/8 in joint: 30 + 10% = 33 sq ft. Each tile plus joint covers 3.125 × 6.125 ÷ 144 = 0.1329 sq ft, so you need 33 ÷ 0.1329 = 248.3 → 249 tiles. Ignoring the joint (0.125 sq ft per tile) would give 264 — about 6% more than needed. In a box of 100, that's 3 boxes either way, but on larger jobs the difference adds up.
Waste allowance by layout
| Layout | Typical extra |
|---|---|
| Straight (grid) or simple offset | 10% |
| Diagonal (45°) | 15% |
| Herringbone, chevron or complex patterns | 15–20% |
| Small rooms with many cuts, or large-format tile | Add a few percent more |
Diagonal and herringbone layouts produce triangular and angled offcuts at every wall, and large tiles waste more per cut because each offcut is bigger. Breakage during cutting and shipping is common enough that buying exactly the calculated number is risky.
Common tile sizes
| Nominal size | Face area per tile | Tiles per 10 sq ft (no grout) |
|---|---|---|
| 3 × 6 in subway | 0.125 sq ft | 80 |
| 4 × 4 in | 0.111 sq ft | 90 |
| 12 × 12 in | 1 sq ft | 10 |
| 6 × 24 in plank | 1 sq ft | 10 |
| 12 × 24 in | 2 sq ft | 5 |
| 18 × 18 in | 2.25 sq ft | 4.4 |
| 24 × 24 in | 4 sq ft | 2.5 |
Nominal sizes are often slightly different from actual sizes — many "12 × 24" porcelain tiles are actually made to metric dimensions of about 11.8 × 23.6 in. For the most accurate count, enter the actual size from the box as a custom size. Box coverage varies widely between products (roughly 10–16 sq ft is common, but not universal), so always use the figure on your carton.
Buying tips
- Buy from the same lot. Tile is made in production runs that can vary slightly in shade and in size (caliber). Check that every box has the same lot or shade code, and buy enough for the whole job at once.
- Keep spare tiles. Holding back a few tiles — or a full box on a large floor — lets you replace a cracked tile later with a perfect match, since the exact lot may be discontinued.
- Grout and thinset are separate purchases. How much you need depends on tile size, joint width, tile thickness and trowel notch, so use the coverage chart on the bag or the manufacturer's online calculator for your specific product.
- Large-format tile and offsets. Long tiles often have a slight bow, so manufacturers commonly recommend an offset of no more than one-third of the tile length to avoid uneven edges (lippage). Check the box for the maker's guidance.
- Laying plank flooring instead? The flooring calculator works out boxes of laminate, vinyl plank and hardwood.
Frequently asked questions
How many 12×24 tiles do I need for 100 sq ft?
Each 12 × 24 tile is 2 sq ft, so 100 sq ft needs 50 tiles with no waste. With a 1/8 in grout joint and 10% extra, the count is 110 ÷ 2.031 = 54.2, so 55 tiles.
How much extra tile should I buy?
About 10% for a straight layout and 15% or more for diagonal or herringbone patterns. Small rooms with lots of cuts and large-format tiles may need a little more.
How many square feet are in a box of tile?
It depends entirely on the product. Many boxes hold roughly 10–16 sq ft, but large-format and mosaic tiles differ. The coverage is printed on the carton, along with the tile count.
Does grout width change how many tiles I need?
Slightly. Each tile covers its own size plus one joint. With 12 × 24 tile and a 1/8 in joint the effect is about 1.5%; with 3 × 6 subway tile it's about 6%.
Why should all my tile come from the same lot?
Different production runs can vary in shade and exact size. Mixing lots can show as a visible color shift or uneven grout lines, so check the lot or shade code on every box.