You quoted 18 m² of tiles because that is the floor. The boxes are 1.44 m². You order 13 boxes on the nose. Mid-job you are two tiles short, pattern does not match, and you are back at the merchant in the van. That trip is wastage you refused to put on the quote.
The formula
Buy quantity = net measure × (1 + wastage %) → round up to pack size
| Material | Typical wastage |
|---|---|
| Facing brick / block (straight walls) | 5% |
| Plasterboard, timber lengths | 8–12% |
| Ceramic / porcelain tiles (straight lay) | 10% |
| Tiles on the diagonal, or a busy pattern | 15% |
| Paint (open a new tin rather than run out) | 1 extra tin |
| Cable / pipe (bends, drops, offcuts) | 10% |
These are starting points, not a British Standard. A tiny cloakroom with more cuts than field can need more than a long hallway.
Worked example
Hall floor: 18 m² net. Porcelain, straight lay, 10% waste. Box covers 1.44 m².
| Step | Number |
|---|---|
| Net area | 18.0 m² |
| Plus 10% waste | 19.8 m² |
| Boxes at 1.44 m² | 13.75 |
| Buy | 14 boxes |
14 boxes — not 13, and not “about 18 m²”.
What people miss
Wastage is not markup. Ten percent more tiles is quantity. Twenty percent on the ticket is handling. Do both, in that order, or you will short the job and still undercharge the run.
Pack size beats the percentage. 13.1 boxes is 14 boxes. The 0.9 leftover still came out of your card.
Pattern and waste are not the same as snagging. A cracked tile in the box is wastage. A customer who changes the border after you have cut it is extra work — quote it.
Leftovers are not a bonus. Half a tin of a discontinued colour is scrap. Price the tin you will actually open.
Related guides
FAQ
- Can I skip wastage on a tiny job?
- No. A small job has more cuts per square metre. The percentage often goes up, not down.
- What if I have leftover from the last job?
- Use it if it is the same batch and the customer accepts it. Do not assume last month’s boxes will match.
- Should wastage appear as its own line on the quote?
- It does not have to. The customer can see a materials quantity that already includes it. You need the working.
- Is 10% enough for everything?
- No. It is a common tile and board floor. Diagonals, natural stone, and awkward rooms need more.
