What are the units for specific gravity?

• A. g/L
• B. g/dL
• C. mL/g
• D. None of the above

Answer: (D)

Specific gravity is the ratio of the density of a sample to the density of water used as a reference. Because both densities are measured in the same units, those units cancel in the ratio, leaving a pure number with no units. That makes specific gravity dimensionless. The options shown are units of density (g/L, g/dL) or a reciprocal density (mL/g), which do not apply to SG. In practice, SG is reported simply as a number, such as 1.020, with no units. Therefore none of the listed units are correct.