Soil Bulking Explained: Excavated, Loose and Compacted Volumes
Understand soil bulking and fill factors through a worked volume example. Distinguish in-place excavation, loose transport volume and compacted fill.
A useful starting point
Calculate the geometric void first, then apply the correct explicitly defined factor. Bulking and loose-to-compacted supply ratios describe different states; material-specific evidence is needed before using either for a real order.
Excavated soil can occupy a different volume after it is loosened. Fill delivered loose can occupy a different volume after compaction. These changes are not extra geometric depth; they are changes in the material's state.
British Columbia's trades training reference discusses soil bulking. The Landscape Design Institute's reference distinguishes bulking, shrinkage and bulk-density concepts. Use project-specific material information rather than treating an example factor as a test result.
Define the state beside every number
Write “in place,” “loose” or “compacted” next to volumes in the estimate. A supplier's cubic metre and a measured void are not necessarily in the same state.
The tool defines bulking as loose volume divided by in-place volume. Its fill factor means loose supply volume divided by compacted target volume. Both factors are at least one in this model.
Work a rectangular void
Assume a simple 4 × 3 m void, 0.6 m deep.
| Quantity | Calculation | Result |
|---|---|---|
| Geometric void | 4 × 3 × 0.6 | 7.2 m³ |
| Loose excavation at chosen 1.25 factor | 7.2 × 1.25 | 9 m³ |
| Loose fill for the same target at chosen 1.15 factor | 7.2 × 1.15 | 8.28 m³ |
The last two rows are separate questions. Do not add 9 and 8.28 m³ and call the result the void volume. Nor do these hypothetical factors prove that the excavated material is suitable for reuse as fill.
Enter the dimensions and explicitly chosen factors in the excavation and fill calculator.
Distinguish a percentage from a multiplier
A 25% volume increase is a multiplier of 1.25, not 25 or 0.25. If a source defines shrinkage in the opposite direction, convert the definition carefully before using the tool's loose/compacted input.
Keep factor evidence with the estimate: material, condition, test or supplier basis and the state being compared.
Check the geometric scope
The tool covers simple rectangular and cylindrical voids. Battered sides, trenches with changing sections, working space and complex ground levels need another geometric takeoff.
This calculation is not an excavation method, shoring design or a decision about ground stability. Use the appropriate project documents for those matters.
Questions for ordering and reuse
Can loose volume be converted straight to tonnes?
Only with the relevant loose bulk density. Rolawn's topsoil guidance notes that composition affects volume-to-weight conversion. The gravel and soil guide keeps that input explicit.
Does fill volume include compaction design?
No. The factor is an estimating input, not proof of achieved compaction or material suitability. Keep geometric quantities separate from the concrete volume and other later construction layers.
