How to use this calculator
- Measure the area to be tiled. For a floor, that is the room. For a backsplash or a shower, split it into rectangles — one per wall, one for the return above the hob — and add a section for each.
- Pick the layout. This sets the waste allowance, which is the part of the calculation people get wrong. You can type over the percentage.
- Enter the coverage printed on the box. Tile is sold by area covered, not by count, and the figure differs between tile sizes and manufacturers. The default here is a placeholder; the box is the authority.
The formula
area to tile = measured area × (1 + waste %)
boxes = area to tile ÷ coverage per box, rounded up
Worked example — a 10 ft × 12 ft floor in a straight layout, tile at 15 sq ft per box:
- Area: 10 × 12 = 120 sq ft
- With 10% waste: 120 × 1.10 = 132 sq ft
- Boxes: 132 ÷ 15 = 8.8, so 9 boxes
Change nothing except the layout — herringbone instead of grid — and it becomes 138 sq ft, which is still 10 boxes rather than 9. That single dropdown is worth more than the rest of the page.
Waste allowances
| Layout | Allowance |
|---|---|
| Straight / grid | 10% |
| Diagonal or herringbone | 15% |
| Complex room, many cuts | 20% |
The allowance is not padding. It is covering two specific things.
Edge cuts. Every tile that meets a wall gets cut, and the offcut is only reusable if another edge happens to need that exact width. In a grid layout the cuts are all the same size along a given wall, so some offcuts do get used. In a diagonal or herringbone layout, every perimeter tile is a different triangle, and almost nothing is reusable — which is the entire reason that figure is higher.
Breakage. Tiles crack while being cut, especially large-format porcelain and anything with a natural stone face. If you are cutting with a manual score-and-snap tool rather than a wet saw, be generous.
Complex rooms are the twenty percent case: a bathroom where the floor has to work around a vanity, a toilet flange, a shower kerb and a doorway is mostly cuts.
Buy one more box than the number, and keep it
This is the single most useful thing on this page.
Tile is fired in batches. Colour and dimension vary slightly between them — enough to see when two batches sit side by side on the same floor. Manufacturers print a batch or shade number on the box precisely because of this, and retailers cannot guarantee matching batches on a reorder.
Product lines are also discontinued regularly. A tile bought this spring may simply not exist in two years.
So: order the calculated number, add a box, and put the unopened one somewhere dry. When a dropped pan cracks a tile in year four, that box is the difference between a half-hour repair and a conversation about replacing the whole floor.
Grout and adhesive
Neither scales with area alone, which is why this calculator does not guess at them.
Adhesive depends on the trowel notch, which depends on tile size and how flat the substrate is. Large-format tile needs a deeper notch and often back-buttering, which can easily double consumption over the bag’s stated coverage.
Grout depends on tile size and joint width together. Large tiles with narrow joints use very little; small mosaics with wide joints use a surprising amount, because the joint length per square foot is enormous.
Both bags print coverage tables. Take the area figure from this page and read the quantity off the bag — that is more reliable than any general rule.
Measuring walls and backsplashes
For a backsplash, measure from the worktop to the underside of the cabinets, and treat each run of wall as its own section. Do not deduct for outlets and switches; they are small, you will cut around them, and the offcuts are waste anyway.
For a shower, measure each wall separately and include the kerb and any niche returns. Shower tiling generates more cuts than any other job in the house — use the twenty percent allowance and do not feel clever about it.
What this does not tell you
It gives you a quantity, not a layout. If your pattern needs to be symmetrical — a feature wall, a herringbone floor that has to land cleanly at a doorway, a backsplash where the top course must not end in a 10 mm sliver — that is a setting-out problem, solved by drawing the tile grid on the wall before any adhesive comes out, not by knowing the total.
This is an estimate. The coverage on your box governs. Enter that figure rather than the default, add the waste for the layout you are actually laying, and buy the spare box.