What does specific gravity measure?

• A. the ratio of density to mass
• B. the ratio of the density of a substance to the density of water
• C. the ratio of volume to mass
• D. the ratio of vapor pressure to temperature

Answer: (B)

Specific gravity expresses how dense a substance is compared with water. It’s calculated by dividing the substance’s density by the density of water at a reference temperature (usually 4°C). Because water’s density is about 1 g/cm³ at that temperature, the value is essentially a unitless ratio that tells you how heavy the material is relative to water. This helps you predict behavior in water (whether it sinks or floats) and compare different substances without dealing with units. The other ideas described don’t describe density relative to water, so they don’t capture what specific gravity measures.