Backfill Material Quantity Calculator
Estimate the loose and imported material required to replace excavation voids after allowing for structures, compacted finished volume and the amount of suitable material available on site.
Backfill geometry and material
Backfill material result
Backfill quantity method
The calculator starts with excavation geometry, subtracts permanent occupied volume and treats the remaining void as the compacted backfill target.
Compacted backfill target = excavation volume − occupied volume
Loose fill required = compacted target ÷ (1 − shrinkage)
Imported fill = max(0, loose fill required − suitable on-site material)
Worked example
A 30 × 1.2 × 1.5 m excavation has 54 m³ gross volume. After 12 m³ of permanent occupied volume, 42 m³ remains to be backfilled. With 12% shrinkage, about 47.73 m³ of loose fill is required before deducting suitable reusable material.
Why occupied volume matters
Foundations, pipes, ducts, drainage components or other permanent works may occupy part of the excavation. Failing to deduct them can overstate the backfill requirement.
Why imported fill is not always the full gap
Suitable excavated material may be reused, but only when it meets the project's material and compaction requirements. The reusable input keeps that assumption explicit.
Truck loads
Where an imported quantity is known, dividing it by truck capacity provides a simple procurement and logistics estimate. Actual truck payload limits and loading practices may govern.
Frequently Asked Questions
Does occupied volume reduce backfill?
Yes.
Does compaction increase loose material required?
Yes.
Can excavated soil be reused?
Only when it is suitable.
Can truck loads be estimated?
Yes.