Swell Factor Calculator

About the Swell Factor Calculator

When undisturbed soil is excavated, it loosens and expands in volume. This expansion is called swell, and it's one of the most critical factors in earthwork estimating. The swell factor determines how much more volume you'll have to haul away compared to the volume you measured in the ground.

Different soil types swell different amounts. Sand expands 10–20%, clay 30–40%, and rock can swell 40–70% when broken into fragments. This calculator converts bank (in-place) volume to loose (after-excavation) volume using the swell factor for your specific soil type.

Accurate swell calculations prevent expensive trucking surprises. If you measure 100 cubic yards in the bank and plan trucking for only 100 CY, you'll be 20–40% short on truck capacity when the material swells after excavation.

When This Page Helps

Swell directly affects your hauling costs. A 30% swell means you need 30% more truck loads than the in-ground volume suggests. This calculator converts bank volume to loose volume so your hauling estimates are accurate from the start.

How to Use the Inputs

1. Enter the bank (in-place) volume in cubic yards.
2. Select the soil type or enter a custom swell factor.
3. Review the loose (swelled) volume.
4. See the volume increase from swell.
5. Use the loose volume for hauling and truck estimates.
6. Check the shrinkage factor if placing material as compacted fill.

Example Calculation

Tips & Best Practices

• Sand and gravel swell 10–20% (factor 1.1–1.2).
• Loam and silt swell 20–30% (factor 1.2–1.3).
• Clay swells 30–40% (factor 1.3–1.4).
• Blasted rock swells 40–70% (factor 1.4–1.7).
• Always use loose volume for trucking estimates, not bank volume.
• The swell factor is the inverse of the shrinkage (compaction) factor when material is recompacted.

Swell Factors by Material Type

Sand: 1.10–1.20. Gravel: 1.12–1.18. Loam: 1.20–1.30. Clay: 1.30–1.40. Hardpan: 1.40–1.50. Blasted rock: 1.50–1.70. These are typical ranges — actual values depend on moisture, gradation, and site-specific conditions.

Bank, Loose, and Compacted Volume

Three volume states exist for earthwork: Bank (undisturbed in the ground), Loose (after excavation), and Compacted (after placement and compaction as fill). Each state has a different volume for the same mass of soil. Converting between states requires swell and shrinkage factors.

Practical Applications

Use bank volume when measuring the hole to be dug. Use loose volume when estimating trucks needed. Use compacted volume when calculating how much fill material to order. Getting the right conversion factor for each stage prevents costly errors in your earthwork estimate.

Common Mistakes

The most common error is using bank volume for hauling estimates. This underestimates truck needs by 10–40%. Another mistake is ignoring the difference between loose and compacted volume when reusing material as fill — one cubic yard of cut does not fill exactly one cubic yard of fill requirement.

Frequently Asked Questions

• What is a swell factor?

  The swell factor is the ratio of loose (excavated) volume to bank (undisturbed) volume. A factor of 1.3 means soil increases 30% in volume when dug up. It accounts for air entering the loosened material.

• Why does soil swell when excavated?

  In its undisturbed state, soil particles are tightly packed with minimal air voids. Excavation loosens the soil structure, allowing air to fill the spaces between particles. This increases the total volume of the material.

• What is the swell factor for clay?

  Clay typically has a swell factor of 1.3–1.4, meaning it expands 30–40% when excavated. Wet, heavy clay swells more than dry clay. Always verify with your geotechnical report for site-specific values.

• Does swell reverse when soil is compacted?

  Mostly, yes. When loose soil is placed as fill and compacted, it returns to near its original bank volume. However, it rarely compacts to exactly the bank density, so there's usually a small net volume gain (5–10%).

• How is swell factor determined?

  Swell factors are determined from the soil's in-place density and loose density, measured through laboratory testing. Published tables provide typical values by soil type, but site-specific testing is more accurate.

• What is the difference between swell and shrinkage?

  Swell is the volume increase when soil is excavated (bank to loose). Shrinkage is the volume decrease when loose soil is compacted (loose to compacted). They are opposite processes but not exact inverses due to compaction variations.

• Does swell factor affect cost?

  Yes, significantly. Hauling is often priced per truck load or per cubic yard. If your swell factors are 30%, you need 30% more trucks than the bank volume suggests. This directly increases your hauling budget.

• What is bank cubic yards vs. loose cubic yards?

  Bank cubic yards (BCY) measure soil in its undisturbed, in-place condition. Loose cubic yards (LCY) measure the same soil after excavation, when swell has increased its volume. Hauling and disposal use LCY.