Tile Calculator
Tile counts have to allow for the grout gap, because each tile occupies its own size plus the joint beside it. Skip that and a large floor comes up short.
Tiles needed
108tiles
- Area
- 100.0 sq ft
- With waste
- 110.0 sq ft
- Square metres
- 10.22
- Tiles
- 108
- Includes a 10% waste allowance. The bare figure is 100.00 sq ft.
- The grout gap is added to each tile's footprint, which is why a wide gap noticeably reduces the count on a large floor.
- Ten per cent covers cuts on a straight lay. Allow fifteen for a diagonal, and buy a spare box from the same batch — colours shift between production runs.
About the tile calculator
A twelve-inch tile with a three-millimetre gap takes up 12.12 inches of floor, so a hundred square feet fits 99 tiles rather than 100. On one tile the difference is nothing; across a floor it is real, and it grows quickly with wider joints and smaller tiles. Mosaic with a five-millimetre joint can shift the count by ten per cent.
Waste goes on top of that. Every tile meeting a wall gets cut and the offcut is rarely usable elsewhere, so ten per cent is right for a straight lay in a square room and fifteen for a diagonal, where every edge tile is cut at an angle.
One thing worth doing beyond the arithmetic: buy the spare from the same batch. Tile colour shifts noticeably between production runs, so a replacement bought a year later rarely matches.
What it works out
- Tile count, with the grout gap allowed for
- Area in square feet and square metres
- Floors or walls, in any tile size
The formula
Tiles = (Area × (1 + Waste)) ÷ ((Tile width + Gap) × (Tile height + Gap))
A tile does not occupy its own size on the floor. It occupies its size plus the grout gap around it, and that is the step most tile calculators skip.
The effect is small on one tile and large on a floor. A twelve-inch tile with a three-millimetre gap takes up 12.12 inches of floor, so a hundred square feet fits 99 tiles rather than 100. Wide gaps and small tiles make the gap matter far more: mosaic with a five-millimetre joint can shift the count by ten per cent.
Waste goes on top. Every tile meeting a wall gets cut, and the offcut is rarely usable elsewhere. Ten per cent is right for a straight lay in a square room; fifteen for a diagonal, where every edge tile is cut at an angle and nothing can be reused.
- Area
- Length times width of the floor or wall being tiled.
- Tile size
- The tile's own dimensions, as sold. A "12 inch" tile is usually very slightly under.
- Gap
- The grout joint. Two to three millimetres on walls, three to five on floors.
- Waste
- Extra for cuts. Ten per cent straight, fifteen diagonal.
A worked example
A ten by ten floor in twelve-inch tiles, three-millimetre grout gap, straight lay.
That works out to 108 tiles.
- Area
- 100.0 sq ft
- With waste
- 110.0 sq ft
- Square metres
- 10.22
- Tiles
- 108
Questions
How many 12x12 tiles do I need for 100 square feet?
About 99 with a three-millimetre grout gap, before waste — the gap means each tile occupies slightly more than a square foot. With a ten per cent allowance for cuts you would buy 108.
Does the grout gap really change the count?
On a large floor, yes. A three-millimetre joint on twelve-inch tiles is about a three per cent difference, and wider joints or smaller tiles push it into double figures. On a single small splashback it is negligible.
How much extra tile should I buy?
Ten per cent for a straight lay, fifteen for a diagonal or herringbone. Buy the spare from the same batch — tile colour shifts noticeably between production runs, so a replacement bought later rarely matches.
What grout gap should I use?
Two to three millimetres for wall tiles and three to five for floors. Rustic and handmade tiles have less consistent edges and need a wider joint to look right; rectified tiles can go tighter.
How do I tile a wall with a window or door in it?
Work out the full wall area, then subtract the opening as its own rectangle. Keep the waste allowance on the full area though — the tiles around an opening all need cutting, so an opening creates waste rather than saving tile.
Should I count tiles or boxes?
Buy by the box, since that is how they are sold. Divide the tile count by the tiles per box printed on the carton and round up.