Specific density is the ratio of the mass versus the volume of a material.

Density vs. gravity

Specific density is based upon units of mass and volume, while

specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water (molecule), wa ...

is dimensionless.

References

Physical quantities Density Volume Ratios {{Physics-stub