Earthwork / Volume conversion
Soil Swell Factor and Shrinkage Calculator
Use this swell factor calculator to convert a known soil volume between bank, loose and compacted states. Enter the swell and shrinkage percentages supplied for your project. The tool calculates equivalent volumes and conversion multipliers, not a site-specific soil factor.
Convert earthwork volumes
Enter one known volume and your project percentages. The starting values of 100 m³, 25% swell and 10% shrinkage are an example, not recommended soil factors.
Known quantity and factors
Increase from bank to loose volume. Enter 25 for 25% swell, not the 1.25 multiplier.
Reduction from bank to compacted volume. Enter 10 for 10%, not a density-test compaction target. Use 0 to less than 100%; compacted volume above bank is outside this model.
Equivalent volumes
- Bank volume
- 100 m³
- Loose volume
- 125 m³
- Compacted volume
- 90 m³
Conversion factors
- Bank to loose
- 1.25 ×
- Loose to bank (load factor)
- 0.8 ×
- Bank to compacted
- 0.9 ×
- Loose to compacted
- 0.72 ×
Method
Soil swell factor formula and volume conversions
Bank volume describes material in its original, undisturbed position. Loose volume describes excavated or hauled material. Compacted volume describes placed and compacted fill. The calculator first determines the equivalent bank volume, then applies each factor from that common basis.
The bank-to-loose swell multiplier is 1 + swell percentage ÷ 100. For example, 25% swell gives a multiplier of 1.25. Shrinkage uses the same bank basis, so do not subtract the shrinkage percentage directly from loose volume.
- Loose volume = bank volume × (1 + swell ÷ 100)
- Compacted volume = bank volume × (1 − shrinkage ÷ 100)
- Bank volume from loose = loose volume ÷ (1 + swell ÷ 100)
- Bank volume from compacted = compacted volume ÷ (1 − shrinkage ÷ 100)
Worked example
Example: 100 m³ measured in the bank
With 25% swell, 100 m³ of bank material becomes 125 m³ loose. With 10% shrinkage measured from the same bank quantity, its compacted volume is 90 m³. Converting directly from loose to compacted requires a factor of 0.72.
If you already know the loose volume, work backwards first: 125 ÷ 1.25 = 100 m³ bank. Then 100 × 0.90 = 90 m³ compacted. Starting with a required compacted quantity works the same way: 90 ÷ 0.90 = 100 m³ bank, which becomes 125 m³ loose.
| Known quantity | Bank volume | Loose volume | Compacted volume |
|---|---|---|---|
| 100 m³ bank | 100 m³ | 125 m³ | 90 m³ |
| 125 m³ loose | 100 m³ | 125 m³ | 90 m³ |
| 90 m³ compacted | 100 m³ | 125 m³ | 90 m³ |
Factor selection
Use project-specific soil factors
Volume change depends on the material, its initial density, moisture, excavation method, handling, and compactive effort. FHWA guidance recommends using factors supplied through geotechnical information and notes that estimating values can vary materially. This calculator therefore does not select a factor from a generic soil preset.
Confirm whether your project expresses the value as a percentage, multiplier, load factor, or yield factor. Here, swell is entered as a positive increase from bank to loose volume, and shrinkage is entered as a positive reduction from bank to compacted volume. For example, enter 25 for a 25% swell and 10 for a 10% shrinkage.
| Value | Example | How to use it |
|---|---|---|
| Swell percentage | 25% | Enter 25 in Swell (%). |
| Bank-to-loose multiplier | 1.25 | Multiply bank volume by 1.25 to get loose volume. |
| Loose-to-bank load factor | 0.80 | Multiply loose volume by 0.80 to recover bank volume. |
| Shrinkage percentage | 10% | Enter 10 in Shrinkage (%). |
| Bank-to-compacted multiplier | 0.90 | Multiply bank volume by 0.90 to get compacted volume. |
| Loose-to-compacted multiplier | 0.72 | Multiply loose volume by 0.72 to get compacted volume. |
Using the result
Carry the correct volume state into the next estimate
- Bank volume is the in-place quantity used for excavation takeoff and may be the measured quantity for payment when the project documents say so.
- Loose volume is the appropriate volume basis for truck bodies, stockpiles, and haul planning. Enter it in the Excavation Haul Cycle and Fleet Calculator.
- Compacted volume is the placed fill quantity. Use it when comparing the required finished fill with available material.
Keep the state label with every quantity. A value of 100 m³ is ambiguous unless it is identified as bank, loose, or compacted.
If your starting point is trench dimensions rather than a known volume, use the Trench Bedding, Backfill and Spoil Calculator to account for pipe displacement, bedding, backfill and soil reuse. That tool already applies swell and shrinkage to its material quantities, so do not apply these factors a second time to its converted results.
Scope
Assumptions and limitations
- Swell means the percentage increase from bank volume to loose volume.
- Shrinkage means the percentage decrease from bank volume to compacted volume.
- The same material mass is assumed across all three states.
- Losses, unsuitable material, over-excavation, settlement, and bulking variation are excluded.
- This tool does not predict moisture-driven movement in expansive foundation soils.
Common questions
Soil swell factor and shrinkage FAQ
What is bank volume?
Bank volume is the volume of material in its original position before excavation. It is commonly identified as BCM or BCY.
Why are swell and shrinkage both based on bank volume?
A common bank basis prevents the percentages from being chained together. Loose and compacted quantities can then be compared consistently.
Can I enter a loose or compacted volume?
Yes. Select the known state and the calculator reverses the corresponding factor to recover bank volume before calculating the other states.
What is the loose-to-bank load factor?
The load factor converts loose volume back to its bank-volume equivalent. It equals 1 ÷ (1 + swell ÷ 100). With 25% swell, the factor is 0.8, so 10 m³ loose represents 8 m³ bank.
Why does the calculator not choose a factor by soil type?
Material labels alone do not establish a project factor. Density, moisture, excavation method, handling, and required compaction can change the result, so the tool requires the factor from your project basis instead of presenting a preset as verified site data.
Does this calculate truckloads?
No. Truck capacity, fill factor, legal payload, and haul-cycle timing require separate inputs and belong in a haul-planning tool.
Calculation basis and source limits
The equations follow percentage changes from a common bank-volume basis. A shrink value of 10% means compacted volume is 90% of bank volume; it does not mean 90% compaction in a density test. This model accepts non-negative shrinkage and does not model materials whose compacted volume exceeds bank volume.
Unit conversions use international feet, inches, and yards. See NIST’s SI conversion-factor reference for the conversion basis; it does not certify this calculator or its construction assumptions.