Which statement correctly describes the relationship between density and specific gravity?

Which statement correctly describes the relationship between density and specific gravity?

• A. Density is weight per unit volume; specific gravity is the ratio of density to water.
• B. Density and specific gravity are the same.
• C. Density is volume per mass.
• D. Specific gravity equals weight per volume.

Answer: (A)

Specific gravity is a comparison of how dense something is relative to water, while density tells you how much mass sits in a given volume. Density is typically expressed as mass per unit volume (for example, kg/m^3). Specific gravity is the ratio of that density to the density of water (at a standard temperature), which makes SG a dimensionless number. If you describe density as weight per unit volume, the same idea still holds because SG uses the density values in a ratio, and the gravity factor cancels. So the statement that density is weight per unit volume and that specific gravity is the ratio of density to water captures the correct relationship. For example, a substance with density twice that of water has SG ≈ 2.

Specific gravity is a comparison of how dense something is relative to water, while density tells you how much mass sits in a given volume. Density is typically expressed as mass per unit volume (for example, kg/m^3). Specific gravity is the ratio of that density to the density of water (at a standard temperature), which makes SG a dimensionless number.

If you describe density as weight per unit volume, the same idea still holds because SG uses the density values in a ratio, and the gravity factor cancels. So the statement that density is weight per unit volume and that specific gravity is the ratio of density to water captures the correct relationship. For example, a substance with density twice that of water has SG ≈ 2.