The formula and a worked example
The math behind this calculator, in two steps:
Area = Length ft × Width ft
Tiles = ⌈ (Area × 144 ÷ Tile area in²) × (1 + Waste) ⌉
Multiplying by 144 converts square feet to square inches, since tile is sized in inches but floors and walls are measured in feet. Dividing by the tile's area (length × width in inches) gives the number of tiles needed to cover the space exactly, and the waste factor adds a buffer for cuts, breakage, and future repairs. The result is always rounded up — there's no such thing as a partial tile on the order form.
Worked example: an 8 ft × 10 ft bathroom floor tiled in 12x12 tiles, with the standard 10% waste allowance:
8 × 10 = 80 sq ft
(80 × 144 ÷ 144) × 1.10 = 88 tiles
Now the same 80 sq ft floor, tiled in larger 12x24 tiles instead — each one covers twice the area of a 12x12, so roughly half as many are needed:
(80 × 144 ÷ 288) × 1.10 = 44 tiles
Bigger tiles mean fewer pieces and fewer grout lines, but they also waste more material per cut — more on that below.
Choosing the waste factor
The waste factor covers cut pieces that end up too small to use, the occasional cracked tile, and a little extra to keep on hand for repairs down the road. How much you need depends on the layout:
- 10% — straight lay: tiles run parallel to the walls in a simple grid. This is the baseline for a rectangular room with a straightforward layout.
- 15% — diagonal or pattern: tiles set at a 45° angle, or a herringbone, basketweave, or other patterned layout. Diagonal cuts along every wall use up more of each tile than a straight cut does.
- 20% — lots of cuts & niches:small or irregularly shaped rooms, layouts with a shower niche, multiple corners, or fixtures to cut around. Bathrooms and other tight spaces often land here even with a straight lay, simply because there's less room for a full tile to fit uncut.
Tile size matters too: larger-format tiles (18x18 and up) waste more material per cut, because trimming a large tile down to fit a small gap throws away a bigger offcut than trimming a small one does. If you're using large-format tile in a room with a lot of cuts, it's worth rounding your waste factor up a notch.
Buying by the box
Tile is sold by the box, and coverage per box is printed on the box itself — commonly somewhere between 10 and 15 square feet, but it varies by tile size and manufacturer, so always check the actual figure rather than assuming. Enter it into the calculator above and it will work out how many full boxes to buy, rounded up — continuing the 8x10 bathroom example, 88 sq ft of tile (with waste) at 12 sq ft per box comes to 8 boxes.
Buy all the boxes for a job from the same dye lot whenever possible. Tile color and shading can shift slightly between production runs, and boxes from different lots can look noticeably different once installed, even if the box label is identical. Most suppliers print a lot or batch number on the box — check that all your boxes match before you start cutting.
It's also worth keeping at least one unopened box after the job is done. Tile gets discontinued, dye lots change, and a chip or crack years later is a much smaller problem if you've got a matching spare on the shelf.
Don't forget the extras
Tile itself is only part of the material list. Also budget for:
- Thinset mortar to bond the tile to the floor or wall.
- Grout to fill the joints between tiles — coverage depends heavily on tile size and joint width, so follow the coverage chart printed on the grout bag rather than guessing.
- Tile spacers to keep joints even and consistent across the whole layout.
- Backer board(cement board or similar) if you're tiling a floor or a wet wall that needs a stable, water-resistant base under the tile.
None of these are optional add-ons in most installs — they're part of the core material list, so price them in alongside the tile itself before you budget the job.