Tile & Flooring Calculator
Work out how many tiles a room needs — and how many boxes to actually buy, which is the number that decides what you spend. Wastage is applied to the area before anything is rounded, the way a tiler would do it.
Three numbers, and only the last one is the one to take to the shop.
- Tiles needed is the area plus wastage, divided by the size of one tile, rounded up. Rounded up because half a tile is a tile.
- Boxes to buy is that count divided by the box size, rounded up again — and this is what the bill is based on.
- Spare afterwards is what those boxes leave you once the room is actually covered.
Measure the room twice before trusting any of it. The commonest expensive mistake in tiling is not the arithmetic; it is a room that turns out not to be rectangular.
Frequently asked questions
Why is the box count the number that matters?
Because it is what you pay for. Shops sell tiles by the box, so needing 74 tiles at ten to a box means eight boxes and eighty tiles. Somebody who budgeted for 74 is short of money, not short of tiles — and the shortfall is always discovered at the till.
How much wastage should I allow?
Ten per cent for a straight lay, fifteen for a diagonal one, twenty for herringbone. The difference is how much of each edge tile gets cut away: a straight lay loses the strip at the wall, a diagonal one loses two triangles from every perimeter tile, and herringbone cuts almost every piece at the edges. Add more for a room with alcoves, pipework or anything the tiles have to be cut around.
Why apply wastage to the area rather than adding spare tiles?
Because rounding twice loses tiles. Ten square metres of 0.24 m² tiles is 41.7 tiles; round that to 42 and add 10% and you get 47. Add the 10% first — 11 m², which is 45.8 tiles — and you get 46. The second is right, and the first quietly sells you a box you do not need.
What does 'spare afterwards' mean?
How many whole tiles are left once the floor is covered, counted against the room itself rather than the padded figure. The wastage is expected to be cut up and thrown away, so counting it as spare would promise you offcuts you cannot use. Keep the real spares: the line will have been discontinued by the time you crack one.
Does this account for grout lines?
No, and it does not need to. A grout joint is two or three millimetres, which makes each tile cover very slightly more than its own size — an effect far smaller than the wastage allowance already covering it.
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