Waste has different causes
Cutting, breakage, selection, layout complexity and uncertain site dimensions are different reasons for extra material.
Simple layouts can need less
Large rectangular areas using repetitive products can often reuse offcuts more effectively than small or irregular spaces.
Complex patterns can need more
Diagonal tiling, herringbone layouts, hips and valleys, or rooms with many corners can generate more unusable cuts.
Pack rounding can exceed the percentage
Even a precise estimate may require an extra pack or stock length. Treat purchasing-unit rounding separately from the selected waste allowance.
Use the numbers in a calculator
Accuracy note
Where a figure depends on a product, supplier, installation method or project specification, use the current information for the exact material being purchased. The reference pages explain the maths and estimating logic; they are not a substitute for current technical data.