Buying stone for a large project: how to calculate area, waste and order quantity
On a large project, a small error in the area calculation can turn into tens or hundreds of square metres of shortage or surplus.
So the order should not be based only on the drawing area.
Step 1: separate the spaces
Break the area down by application:
- floors
- façade
- stairs
- walls
- skirting
- landscaping
Each has a different waste rate.
Step 2: net area
First calculate the net installable area.
Step 3: waste
Waste depends on:
- tile size
- the shape of the plan
- corners
- the laying pattern
- veining
- book-matching
There is no fixed percentage that fits every project.
A simple example
If the net floor area is 1,000 m² and the project layout creates about 7% waste, the base order will be roughly 1,070 m².
This number must still be confirmed against the actual drawings.
Calculate stairs separately
Stairs are not simple square metres.
Count treads, risers and landings separately.
Slabs
For slabs it is better to design the actual cutting layout rather than use an approximate percentage.
Top-up stock
On large projects some spare stock can help with:
- breakage
- future repairs
- design changes
Phased purchasing
If the project has several phases, you need to choose between:
- buying the whole quantity
- buying in stages
Buying in stages increases the risk of grade differences.
Grade
The larger the surface, the more visible colour differences become.
See how to choose the right stone grade.
One batch or several?
If colour consistency is critical, sourcing the main quantity from one production run is an advantage.
Delivery schedule
Do not bring all the stone to site earlier than needed if you do not have suitable storage.
Storage
Stone should be stored where it:
- will not be damaged
- will not get dirty
- stays accessible for installation
Check every shipment
For each shipment, record:
- quantity
- dimensions
- grade
- breakage
- match with the order
Project buying and price
On a large project, price is only one factor.
- supply reliability
- timing
- quality control
- transport
all matter a great deal.
Purchase plan table
| Area | Net area | Waste | Order quantity | Delivery |
|---|---|---|---|---|
| Floors | ||||
| Walls | ||||
| Stairs | ||||
| Façade |
Common mistakes
- Using one waste percentage for every space
- Buying phase one without a plan for top-up stock
- Ordering in stages without controlling the grade
- Not calculating stairs separately
- Buying far too early
- Not checking shipments
Summary
On a large project, the net area is only the starting point.
The real order quantity should be set by the layout, waste, phasing and the need for top-up stock.
Before ordering, see ready stock vs factory production.
Frequently asked questions
What waste percentage should I allow?
There is no fixed number; it depends on the layout and the dimensions.
Should I buy all the stone at once?
If grade consistency matters, coordinated buying helps, but storage and the installation schedule must also be considered.
Is top-up stock necessary?
It is useful on many projects.