About this tool Calculate relative density (Dr) — also called density index (Id) — of granular soils. Enter maximum and minimum void ratios (or dry densities) along with the in-situ value to determine how dense the soil is relative to its loosest and densest states.
Relative density is the primary index for describing the state of granular soils. It directly correlates with shear strength, stiffness, and liquefaction resistance.
Standards: BS 1377-4 (maximum and minimum density tests), BS EN ISO 14688-2 (classification).
How to use this tool 1. Select input mode — void ratios or dry densities.
2. Enter maximum and minimum values — from BS 1377-4 tests (loosest and densest states).
3. Enter the in-situ value — from undisturbed sampling or in-situ test correlation.
Technical information Dr = (emax - e) / (emax - emin) × 100%
From dry densities: Dr = (ρd,max / ρd) × (ρd - ρd,min) / (ρd,max - ρd,min) × 100%
Classification: 0–15% Very loose | 15–35% Loose | 35–65% Medium dense | 65–85% Dense | 85–100% Very dense
Limitations emax and emin tests have inherent variability. Different operators and methods can give different values, which directly affect Dr.
Relative density is only meaningful for clean, coarse-grained soils (sands and gravels with <15% fines). It is not applicable to clays or silts.
In-situ void ratio is difficult to measure directly. Dr is often estimated indirectly from SPT N or CPT qc correlations rather than measured.
Revision history 16 June 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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