Bulked Soil Volume Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 10/10/2026
The bulked volume of excavated soil is calculated with in-situ volume × bulking factor. For 18 m³ of in-situ soil with a common factor of 1.2, the bulked volume reaches 21.6 m³, meaning 3.6 m³ more to haul away or store.
Explanation
Excavated soil always takes up more volume than it did in place in the ground, because it loses the natural compaction it had before being dug out: this phenomenon, called bulking (or swell), must be accounted for to correctly size the number of dump trucks or skips needed to haul material off a job site. Our excavation volume calculator gives the in-situ volume (that of the pit or trench itself), but doesn't calculate the actually bulked volume once the soil is out of the ground — that's exactly what this calculator does, by multiplying that in-situ volume by a bulking factor. This factor varies greatly depending on the soil type: light topsoil generally bulks by 10 to 20%, clay or silt by 20 to 35%, sand or gravel by 10 to 15%, while fragmented rock can bulk by 50 to 70% or more. Absent a single, fully consistent table across technical sources for these precise values by soil type, this calculator leaves the factor as an adjustable input, with a default benchmark of 1.2 (i.e. 20% bulking), a common simplified flat-rate value for ordinary soil. For a real project, the value used in the geotechnical study or by the earthworks contractor remains the reference to favor, with an extra safety margin if the soil hasn't been precisely characterized.
Example: 18 m³ of in-situ soil, factor of 1.2
Inputs
In-situ volume: 18 m³. Bulking factor: 1.2.
Calculation
Bulked volume = 18 × 1.2 = 21.6 m³. Extra volume = 21.6 − 18 = 3.6 m³.
Result
This soil will take up 21.6 m³ once excavated, 3.6 m³ more than its original in-situ volume.
Frequently asked questions
Why does soil take up more volume once excavated?
Because in place in the ground, soil is compacted by the weight of the layers above it and by time, which reduces the voids between particles. Once dug out, it regains a looser structure, with more voids filled with air, which mechanically increases its apparent volume without its mass changing.
Which factor should I choose if I don't know my soil's exact type?
The default value of 1.2 (20% bulking) is a reasonable flat-rate benchmark for ordinary garden soil, but it underestimates the real bulking of compact clay or rock. When in doubt, it's better to use a more conservative value (1.3 to 1.4) to avoid undersizing the number of skips needed for haul-off (see our dumpster size calculator), or ask the earthworks contractor, who generally knows the local soil type.
Does this bulked volume also apply to backfill reused on site?
Yes, the same principle applies: if the excavated soil is reused as backfill on the same site rather than hauled away, it will temporarily take up this extra bulked volume until it's recompacted. Properly compacted backfill generally returns to a density close to its original state, but rarely identical without careful mechanical compaction.