Why the pattern changes how many tiles you buy
Waste in tiling is almost entirely perimeter cuts. Every tile that meets a wall gets cut, and the offcut only gets reused if there happens to be a gap the same size somewhere else. A pattern that produces more cuts, and stranger-shaped cuts, wastes more — it's that simple.
| Layout | Waste | Why |
|---|---|---|
| Straight / grid | 10% | Cuts only where the field meets a wall, and both halves of a cut tile are usable rectangles |
| Brick / offset | 10% | Same cut count, but every second row starts with a half tile — the offcuts still fit somewhere |
| Diagonal 45° | 15% | Every perimeter tile is a triangle. The other half of the triangle only fits in the opposite corner |
| Herringbone | 20% | Two cut angles at every edge, plus the pattern itself has to be set out from a centre line — twice the offcuts of a grid |
Those bands are trade practice, not a rule. Push them up on a small bathroom full of niches or anywhere the setout can't start from a clean line. Push them down on a big square floor where the perimeter is a tiny fraction of the area.
Boxes round up twice
This is where people quietly come up short. You round up to a whole tile — fine, obvious. Then you round up again to a whole box, and that second rounding can add most of a box on its own.
A worked example
A 4m × 3m bathroom floor, 300 × 300 ceramic, laid straight, 3mm joints, 8mm thick, 10 tiles a box.
- Area: 4 × 3 = 12 m²
- Straight lay at 10% waste: 12 × 1.1 = 13.2 m² of tile to buy
- One tile covers 0.3 × 0.3 = 0.09 m²
- Tiles: 13.2 ÷ 0.09 = 146.67 → 147 tiles
- Boxes: 147 ÷ 10 = 14.7 → 15 boxes, which is 150 tiles, so 3 spare
- Grout: ((300 + 300) ÷ 90,000) × 3 × 8 × 1600 ÷ 1000 = 0.256 kg/m², so 0.256 × 12 = 3.07 kg
- Adhesive at 4 kg/m²: 4 × 12 = 48 kg → three 20kg bags
Lay the same room in herringbone and the waste goes to 20%: 14.4 ÷ 0.09 = 160 tiles, so 16 boxes. One extra box, purely for the pattern.
The grout formula, and why it isn't a guess
Grout is joint volume. The first part of the formula, (length + width) ÷ (length × width), is how many millimetres of joint there are in each square metre of floor. Multiply that by the joint's width and its depth and you have the volume of grout in a square metre; multiply by the density of the mixed grout — around 1600 kg/m³ for a cement-based product — and divide by a thousand to land in kilograms.
The practical upshot is that small tiles drink grout and big tiles barely touch it, because small tiles mean far more lineal metres of joint per square metre of floor.
| Tile size | Thickness | Grout at a 3mm joint |
|---|---|---|
| 100 × 100 | 6mm | 0.576 kg/m² |
| 200 × 200 | 7mm | 0.336 kg/m² |
| 300 × 300 | 8mm | 0.256 kg/m² |
| 300 × 600 | 9mm | 0.216 kg/m² |
| 600 × 600 | 10mm | 0.160 kg/m² |
A mosaic sheet is the extreme case — 25mm tiles at a 2mm joint can be over 2 kg/m². If you've ever run out of grout on a mosaic splashback, that's why.
Adhesive by notch size
Adhesive is consumed by the depth of the bed, and the trowel decides that. Uneven substrates and large-format tiles need a bigger notch and often back-buttering as well.
- 6mm notch — about 3 kg/m², small tiles on a flat wall
- 8mm notch — about 4 kg/m², the everyday floor rate
- 10mm notch — about 5 kg/m², bigger tiles or a slightly uneven bed
- 12mm notch — about 6 kg/m², large format
- Back-buttered large format — 8 kg/m² and up, because you're bedding both faces
These are typical figures off Australian adhesive bags. The technical data sheet for the product you're using is the real number and it's worth thirty seconds — the difference between 4 and 6 kg/m² on a 40 m² floor is four extra bags.
Buy the whole job in one batch
Tiles are fired in batches and the shade varies between them. It's not subtle under a bathroom light, and it is absolutely a callback. Buy every box from the same batch number, check the number on every box before you leave the yard, and open several boxes and mix as you lay so any variation within the batch spreads out instead of landing in one corner.
Buy spares beyond what the job needs too. A cracked tile in three years is a fifteen-minute repair if there's a match in the shed, and a whole floor if there isn't — that batch will be long gone.
A few things worth checking before ordering
- Rectified or pressed? Rectified tiles are cut square after firing and can take a 2mm joint. Pressed ceramic needs 3mm or more to absorb the size variation.
- Walls and floor separately. Different tiles, different waste, different adhesive rate. Run the calculator twice.
- Take out what isn't tiled — a hobbed shower base, a built-in bath, an island footprint.
- Waterproofing is its own line, never part of the tiling allowance.
Materials sorted. Now get paid for the job.
Yamate turns tiles, grout, adhesive and your hours into a quote the customer can accept on their phone, then an invoice, then a payment — GST handled and the follow-ups chased for you.
Try Yamate free → Free to try · no card · sign in with a link, no password to rememberTiles, grout & adhesive FAQ
How many tiles do I need for a room?
Divide the area by what one tile covers, after adding the waste your layout generates. A 12 m² floor in 300 × 300 tiles laid straight needs 147 tiles at 10% waste — which is 15 boxes if there are 10 to a box.
How much waste should I allow for tiles?
Ten per cent for a straight or brick-bond layout, fifteen for a 45° diagonal, twenty for herringbone. The pattern decides it, because waste is almost entirely perimeter cuts and fancier patterns cut more awkward shapes.
How much grout do I need per square metre?
It depends on the tile size, the joint width and the tile thickness. A 300 × 300 tile with a 3mm joint 8mm deep works out to 0.256 kg per square metre; a 600 × 600 is only 0.16, and mosaics can be over 2.
How much tile adhesive per square metre?
About 4 kg per square metre with an 8mm notched trowel, which is the everyday floor rate. A 6mm notch is nearer 3, a 12mm notch nearer 6, and back-buttered large format can be 8 or more.
Why do tiles need to come from the same batch?
Shade varies between firing batches, and the difference shows badly under a bathroom light. Buy the whole job in one batch, check the batch number on every box, and mix boxes as you lay so any variation spreads out.
Should I buy spare tiles?
Yes — a box beyond what the job needs. A cracked tile in a few years is a quick repair if there is a match in the shed, and a whole new floor if there is not, because the batch will be long discontinued.
Other calculators you'll want
General information for Australian trades, and an estimate only — not tax, financial or legal advice. It is not engineering, building or design advice either: a calculator works out a quantity from the figures you enter, and anything that needs sign-off still needs your engineer, certifier or building surveyor. Waste bands are trade practice and vary with the room, the setout and the tile. Grout consumption is the standard joint-geometry formula and assumes a mixed density around 1600 kg/m³. Adhesive coverage figures are typical published Australian bag rates and depend on the notch, the substrate and the tile — check the technical data sheet for the product you're using. This is a materials estimate for ordering and quoting, not a specification.