Measure the area in square metres, add 10% for wastage, then divide by the size of one tile. That's the whole method — and it's the same sum I do on every quote, whether it's a downstairs loo or a 40 m² kitchen-diner.
If you'd rather skip the maths, use our tile calculator — put your measurements in and it does the lot, wastage included.
Key takeaways
- Area to tile (m²) ÷ area of one tile (m²) = tiles needed. Add wastage before you divide.
- 10% wastage for straight or brick-bond, 15% for herringbone, diagonal, or large-format tiles.
- Always round up to whole boxes — and keep one spare box sealed for repairs.
- Measure the room in metres, the tile in millimetres (it's on the box).
- For an awkward or L-shaped room, split it into rectangles and add them up.
Step 1: measure the area
Measure the length and width of each surface you're tiling and multiply them. A bathroom floor that's 4m long and 3m wide is 12 m² (4 × 3).
Tiling more than one surface — say all four walls of a shower? Measure each one, work out its area, and add them together. Don't try to be clever with one big sum; do each wall on its own and total them at the end. Fewer mistakes that way.
If the room's an L-shape or has a chimney breast, split it into rectangles in your head, measure each rectangle separately, and add them. That's exactly what the calculator's "add another area" button is for.
Step 2: take off the big gaps
You don't tile over a doorway, a window, or a fitted vanity unit. Measure those, work out their area, and subtract them from your total.
Be sensible about it, mind. Knocking off a single light switch isn't worth the bother — that's what wastage is for. But a 0.8 × 2.1m door opening (1.68 m²) or a big picture window is worth taking off, especially on a wall.
Step 3: add your wastage
Wastage is the spare you order on top, because no job uses 100% of what you buy. Cuts, the odd breakage, a tile that chips on the corner, and a box kept back for future repairs — it all comes out of that margin.
Here's what I add, by lay pattern:
| Lay pattern | Wastage | |---|---| | Straight | 10% | | Brick bond | 10% | | Herringbone | 15% | | Diagonal | 15% | | Large-format (600mm+) in a small room | 15% |
Herringbone and diagonal lays eat more tile because nearly every edge tile gets cut at an angle, and the offcut often can't be used anywhere else. Large-format tiles are similar — fewer tiles overall, but every cut wastes a bigger piece, so a small room can need 15% rather than 10%.
So our 12 m² floor on a straight lay becomes 12 × 1.10 = 13.2 m² to order.
Step 4: divide by the tile size
Now divide your area-to-order by the area of a single tile.
A 600 × 600mm tile is 0.6m × 0.6m = 0.36 m². So:
13.2 ÷ 0.36 = 36.7 → 37 tiles.
Always round up — you can't order 0.7 of a tile, and coming up short mid-job is the one thing you don't want.
Tiles per m², for the common sizes
| Tile size | Tiles per m² | |---|---| | 600 × 600mm | ~2.8 | | 300 × 600mm | ~5.6 | | 300 × 300mm | ~11.1 | | 200 × 250mm | ~20 |
These are bare figures with no wastage — handy for a rough gut-check, but run the real numbers (with wastage) before you buy.
Step 5: round up to whole boxes
Tiles are sold by the box, not the single tile, and box quantities vary with tile size — anything from 3 large-format tiles to a dozen small ones. Check the box quantity on the product, work out how many boxes covers your tile count, and round up to the whole box.
That rounding often nudges you a bit past your 10%, which is fine. The one rule I'd never break: keep a full box back, sealed, after the job. Tile colours are mixed in batches, and a replacement box bought eighteen months later almost never matches. A spare box in the loft is the cheapest insurance there is.
Let the calculator do it
That's the method. If you'd rather not do it on the back of a fag packet, the TileFlow tile calculator runs every step above — multiple areas, door and window subtractions, lay-pattern wastage, the lot — and gives you a tile count in seconds.
Planning the whole job? It's worth getting the subfloor prep and grout choice right too — both make more difference to the finish than people expect.