Planning guide ยท Materials
How Much Extra Material Should You Order?
Waste is not a magic 10%. The right allowance depends on what can be reused, what must be cut, how the product is packaged, and how uncertain the site really is.
Reviewed September 4, 2026Separate geometric waste from project uncertainty
Geometric waste comes from cuts, pattern, and offcuts. Project uncertainty comes from uneven grade, breakage, rejected pieces, measurement limits, and changes. Naming the reason for each allowance makes the final quantity easier to defend and adjust.
- Use lower allowances for simple repeatable layouts.
- Increase for curves, diagonal patterns, and color matching.
- Treat redesign risk separately from normal waste.
Round to the way the supplier sells
A precise calculated quantity is not always a purchasable quantity. Concrete may be ordered in quarter-yard increments, gravel by load or half ton, pavers by layer or pallet, and flooring by carton. Apply the allowance first, then round up to the sale unit.
- Do not round each small room separately unless it requires separate packages.
- Check minimum delivery and short-load charges.
- Keep leftover matching material when future repair is likely.
Do not use waste to cover a missing design
A bigger percentage cannot replace a drainage plan, structural detail, verified thickness, or known excavation profile. When uncertainty is caused by missing design information, resolve the decision or create a separate contingency line rather than burying it in material quantity.
- Confirm compacted depth.
- Price demolition and haul-off explicitly.
- Separate structural extras from surface-material waste.
Document the assumption
Write the raw quantity, allowance percentage, rounded purchasing quantity, and source of the assumption together. That record makes supplier conversations and later changes much easier.
- Date price and coverage inputs.
- Record the exact product or mix.
- Update the estimate when package coverage changes.