How Much Extra Material Should You Buy?
By the TapeMeasureCalc team · Updated · 6 min read
The area of a room is not the amount of tile you need, and the volume of a slab is not the amount of concrete that turns up on the truck. Every material order needs a margin for cutting, spilling, settling and the odd broken piece. Too little and you’re stuck mid-job; too much and the leftovers sit in the garage for years. Here’s how to pick the margin.
Why you can't order the exact amount
- Cuts. Tiles, pavers, boards and sheets get cut at every edge, and an offcut from one side rarely fits the other.
- Breakage. A few pieces crack in transit or during cutting.
- Uneven ground. A subgrade that dips half an inch swallows concrete and gravel.
- Settling and compaction. Mulch, soil and crushed stone all take up less space once they’re watered or rolled.
- Spillage. Some concrete always stays in the chute, the wheelbarrow and the mixer.
Starting points by material
These are common rules of thumb, not standards. Use them as a starting point, then adjust for your site and your installer’s advice.
| Material | Typical allowance | Go higher when… |
|---|---|---|
| Ready-mix concrete | 5–10% | the ground is uneven or the forms are hand-built |
| Floor and wall tile | 10% | diagonal or herringbone layouts, small rooms, large-format or natural stone tiles (15–20%) |
| Pavers | 5% | herringbone, angled patterns or curved edges (10% or more) |
| Drywall / plasterboard | 10% | lots of corners, short walls, sloped ceilings |
| Gravel and road base | 5–10% | the material compacts a lot; ask the supplier |
| Mulch and soil | a little extra, or top up later | the material is light and fluffy |
What running short really costs
The extra material is rarely the expensive part. Running short is. With concrete, a second delivery can mean fresh concrete meeting concrete that’s already started to set, which leaves a weak joint. With tile, a top-up order may come from a different production batch with a slightly different shade, and it shows. With anything delivered, there’s a second delivery charge.
So for most materials, it pays to round up. Bulk materials are the exception worth thinking about: an extra half yard of mulch you don’t need still has to go somewhere.
Leftovers worth keeping
- A few spare tiles, pavers and fence boards, for repairs later. Matching them in five years is hard.
- A small, labelled amount of each paint colour, for touch-ups.
- Unopened bags of concrete or grout, kept dry. Opened bags pick up moisture and don’t keep well.
Waste in the calculators
The calculators that need it have a waste or extra field you can change, with a sensible default: 10% on the tile calculator and concrete calculator, 5% on the paver calculator. Results show the quantity with and without waste, so you can see exactly what the allowance adds.