Calculate the void ratio of soil from specific gravity, water content, and degree of saturation.
Void ratio (e) is the ratio of void volume to solid volume. It is one of the most fundamental soil properties, directly influencing compressibility, shear strength, and permeability. A higher void ratio means a looser, more compressible soil.
This tool is useful for quick cross-checks during ground investigation reporting, lab data review, and preliminary geotechnical design.
Enter specific gravity (Gs) — defaults to 2.65 (quartz sand). Adjust for clay minerals (2.70–2.75) or other soil types.Enter water content (w) — as a percentage, from lab moisture content tests (BS 1377-2).Enter degree of saturation (S) — defaults to 100% (fully saturated, typical below the water table). Reduce for partially saturated soils.Review the result — the void ratio is calculated instantly. Compare against typical ranges shown below the result.The tool uses the standard phase relationship:
e = Gs × w / S where e = void ratio, Gs = specific gravity of solids, w = water content (decimal), S = degree of saturation (decimal).
This identity is derived from the soil phase diagram and is found in all standard geotechnical references including Craig's Soil Mechanics and Das's Principles of Geotechnical Engineering. The canonical form is Se = wGs.
Typical void ratios
Dense sand: 0.4–0.6 Loose sand: 0.6–0.9 Stiff clay: 0.5–0.8 Soft clay: 0.9–1.5+ Limitations Assumes homogeneous soil — natural soils may vary significantly across a sample. Gs should be determined by laboratory testing (BS 1377-2) rather than assumed, particularly for clay-rich or organic soils. For partially saturated soils, accurate determination of S in the field can be difficult; where possible, use saturated conditions (S = 100%) with lab water content for the most reliable result. Revision history 1 April 2026: Initial release.
Disclaimer This tool is provided for educational and general information purposes only. It is not a substitute for professional engineering advice, design or verification.
Diggy and its contributors are not licensed engineering consultants and no results generated by this tool should be used directly for construction, design or safety-critical decisions.
All values and outputs are based on published empirical correlations and should be independently checked and confirmed by a qualified geotechnical engineer before use.
By using this tool, you accept full responsibility for how you interpret and apply the information provided.
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