What Does Specific Gravity (SP.GR) Mean?
Specific gravity is a measurement of the density of a material relative to another material. Specific gravity is expressed as a ratio. A material with a specific gravity greater than 1 will have a higher density than its reference material.
The specific gravity of a material under consideration may be important in a material selection or formulation process. The difference in specific gravity across materials makes it a popular means of sorting, particularly in the mining industry.
Corrosionpedia Explains Specific Gravity (SP.GR)
Specific gravity is an important measurement when considering the density of an unfamiliar material.
The ratio of the unfamiliar material with a more common material allows for quick comparisons in regard to density. For gases, air at normal pressure and temperature is often used as the reference material. For liquids, water is usually used as the reference material.
An example of comparing two liquids is that kerosene has a value lower than 1 compared to pure water at 40°F (104°C) under normal atmospheric pressure. This means that kerosene has a lower density than water at that temperature. This also means that kerosene will float on the water's surface when both are placed in a container.
Specific gravity is a comparison of densities, and as a result no dimensions are required when evaluating and considering specific gravity. What is required to calculate a specific gravity is a material and its density, a reference material and its density, a temperature and a pressure. The reference material and its density must be specified at a given temperature and pressure. Once this is determined, it is assigned a specific gravity of 1. Then, the materials being evaluated will have their densities measured at a given temperature and pressure, and will be designated with numbers less than, equal to, or greater than one depending on their density relative to the reference material.