What is specific gravity?

Answer: A — The ratio of the weight of a volume of liquid or solid to the weight of an equal volume of water

Specific gravity is a way to compare how heavy a material is relative to water using the same volume. It’s the ratio of the material’s density (or weight per volume) to the density (or weight per volume) of water, typically with water’s density used as the reference at 4°C. Because it’s a ratio of two weights (or two densities) under the same gravity, the value is dimensionless. In practice, this means materials with an SG greater than 1 are heavier than water and tend to sink, while those with an SG less than 1 tend to float. This concept is captured by describing it as the ratio of the weight of a volume of the material to the weight of an equal volume of water. The other ideas—density at room temperature, rate of vaporization, or color—do not define specific gravity.