# property>specific **gravity**

## What is Specific **Gravity**?

The Specific **Gravity** of liquids and solids is defined as a dimensionless unit which is the ratio of density of a material to the density of water at a given temperature, where density is defined as the material’s mass per unit volume and is measured in kg/m^{3}. The temperature and pressure of both the material and water need to be the same as these factors influence the density and hence the specific **gravity**. Specific **gravity** is unique to every material and has a very wide range of application. In more general terms specific **gravity** is the ratio of the density of a material to that of any standard substance, although usually this is water at 4 degrees Celsius or 39.2 degrees Fahrenheit. By definition, water has a density of **1** kg per litre at this temperature.

The specific gravities of gases usually are compared to dry air which generally has a density of **1**.29 **g** per litre. The specific **gravity** of all other materials is compared to water as a fraction heavier lighter or heavier density.

### Calculating Specific **Gravity**

The following formula is used to calculate the specific **gravity** of a material.

SG = ρ / ρW

Where SG = specific **gravity**, ρ = density of the material (kg/m^{3}), ρW = density of water ( kg/m^{3}). The reference density of water at 4^{o}C (39^{o}F) is used as the reference as these are the conditions of maximum density.

### Measuring Specific **Gravity**

There is a wide range of instruments designed to measure the specific **gravity** of a material. The hydrometer can be used to measure the specific **gravity** of any liquid. The device is designed to float freely at the liquid surface with a protruding stem giving a reading corresponding to the specific **gravity** of the liquid. Other instruments to measure specific **gravity** are the Pycnometer, and digital density meters based on oscillating U-tubes.

### Applications of Specific **Gravity**

Specific **Gravity** has a wide range of applications including:

- Pharmaceuticals: The specific
**gravity**is used to find out the purity of a drug since each of the constituents has a distinct specific**gravity**. - Determining the additives used in a base material: Specific
**gravity**is used to find out the amount of additives used in a base material which might affect the performance and stability of the base material. - Urine Specific
**Gravity**: The Urine Specific**gravity**(USG) is measured and used mostly in veterinary sciences to understand whether water is excreted or conserved in an appropriate fashion. - Calculating volume of a fluid: The fluid’s volume can be calculated using the specific
**gravity**of the fluid and the weight. Conversely the weight can be calculated if the volume is known. - Other applications of specific
**gravity**include fluid mechanics, buoyancy and the brewing industry.