Calculate all four types of soil unit weight from specific gravity, void ratio, and degree of saturation.
Soil unit weight is essential for calculating overburden stress, effective stress, bearing capacity, earth pressures, and slope stability. This tool computes bulk, dry, saturated, and submerged (buoyant) unit weights simultaneously, in both SI and Imperial units.
Useful during ground investigation reporting, preliminary design, and for quick cross-checks when reviewing geotechnical data.
Select unit system — SI (kN/m³) or Imperial (pcf).Enter specific gravity (Gs) — defaults to 2.65 (quartz sand). Adjust for clay minerals (2.70–2.75) or site-specific test results.Enter void ratio (e) — from laboratory testing or calculated using the Void Ratio Calculator.Enter degree of saturation (S) — affects the bulk unit weight only. Defaults to 100% (saturated). Dry, saturated, and submerged values are independent of this input.Review all four results — bulk (γ), dry (γd), saturated (γsat), and submerged (γ') unit weights are shown together.The tool uses the standard phase relationship formulas:
γ = (Gs + Se) × γw / (1 + e) — bulk unit weightγd = Gs × γw / (1 + e) — dry unit weightγsat = (Gs + e) × γw / (1 + e) — saturated unit weightγ' = (Gs - 1) × γw / (1 + e) — submerged (buoyant) unit weightThe unit weight of water (γw) is taken as 9.81 kN/m³ (SI) or 62.4 pcf (Imperial), following standard geotechnical practice as per Das's Principles of Geotechnical Engineering and Craig's Soil Mechanics.
Note that the saturated unit weight is a special case of the bulk formula when S = 100%, and the submerged unit weight equals γsat − γw.
Limitations Unit weights are bulk properties — natural soils vary with depth and lateral extent. Use representative values for the stratum being analysed. The submerged unit weight formula assumes hydrostatic conditions. For flowing groundwater or seepage conditions, additional analysis may be required. For design purposes, unit weights should be derived from site-specific laboratory testing rather than assumed from typical values alone. 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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