What is the Difference Between Density and Specific Gravity?

Density and specific gravity are related concepts used to describe mass and compare substances, but they are not identical measures. Here are the key differences between density and specific gravity:

• Density is defined as the ratio of the mass (weight) to volume of a substance. It is usually measured in units like grams per cubic centimeter (g/cm³), grams per milliliter (g/mL), pounds per cubic foot (lb/ft³), or pounds per gallon (lb/gal). Density is an absolute quantity and is somewhat dependent on temperature and, to a lesser extent, pressure.
• Specific Gravity is defined as the weight of a sample, at a given temperature, divided by the weight of the same volume of water, at the same temperature or a different specified temperature. It is a ratio with no units, but it is dependent upon both the temperature of the substance and the temperature of the water.

In summary:

• Density is an absolute quantity represented by the ratio of mass to unit volume of matter.
• Specific gravity, also called relative density, is a measure of density with respect to the density of pure water at 4 °C.

When comparing substances, if a substance has a specific gravity less than 1, it will float on water, while a substance with a specific gravity greater than 1 will sink. Density is used in various domestic and commercial applications, while specific gravity is used in industries to measure the concentration of solutions.

Comparative Table: Density vs Specific Gravity

Density and specific gravity are both used to describe mass and can be used to compare substances. However, they are not identical measures. Here is a table highlighting the differences between density and specific gravity:

In summary, density is an absolute value representing the mass of a substance per unit volume, while specific gravity is a relative value comparing the density of a substance to the density of a reference substance, usually water.