Soil weight and volume relationships form the foundation of geotechnical analysis, organizing the three-phase soil system (solids, water, air) into volumetric and gravimetric indices. The diagram maps five core concept areas: soil phases, volumetric ratios, gravimetric ratios, fundamental indices, and soil properties—each defining how phase distribution affects density, water content, void ratio, and compaction state. These relationships enable engineers to determine critical parameters like void ratio (e), porosity (n), water content (w), unit weights (γ), and relative density (Dr) essential for foundation design and soil classification. Fork this diagram to customize soil phase compositions, add site-specific parameters, or integrate into geotechnical reports and educational materials. Understanding these interconnected relationships is vital for predicting soil behavior under load and selecting appropriate foundation types.