What does it mean?
A wastage factor adds a stated allowance to a net material quantity for cutting, handling, breakage or other expected losses. It should be selected for the material and work method. It is different from soil bulking, compaction or design contingency. Keeping the net quantity and allowance visible makes it easier to revise the estimate without losing the original measurement.
In practice
A 3.6 m³ net concrete quantity with a 5% allowance becomes 3.78 m³. If bags yield 0.012 m³ each, the arithmetic order quantity is 315 bags before checking availability and product suitability.
Keep in mind
When preparing an estimate, record the specification reference, units and source of each assumption. Separate the net measured quantity from purchase allowances so changes remain easy to trace. Confirm product dimensions, yields and installation requirements with the supplier. Quantities do not establish structural adequacy or material suitability: use the project’s approved design and details, and seek the responsible designer’s clarification where the specification is incomplete.