What Is Soil Specific Gravity?
A density ratio used across nearly every other geotechnical calculation
What it measures
Specific gravity of soil solids compares the density of the actual solid soil particles (not the soil mass as a whole, which includes air and water in its voids) to the density of water. Common values for most mineral soils cluster in a fairly narrow range, though organic soils and some unusual mineral compositions can fall outside it.
How it's tested
A common laboratory method (such as ASTM D854) uses a pycnometer — a specialized flask of known volume — to measure the volume of water displaced by a known mass of oven-dried soil solids, from which specific gravity is calculated.
Why other calculations depend on it
Specific gravity is a key input for calculating a soil's void ratio, porosity, and degree of saturation — properties that in turn feed into settlement, permeability and strength analyses. It's rarely the final answer engineers need on its own, but it's frequently a required input to get there.
Related Calculators
Related Guides
More From the Blog
Sources
ASTM D854
Standard Test Methods for Specific Gravity of Soil Solids by Water Pycnometer.