Terms such as gravel, sand, silt, and clay are used to indicate grain sizes. These terms are used only as a designation of particle size.

In the particle soil classification system, soils are arranged to the grain size.

Based on particle size, soil can be classified as

As the system is classified based on size, it is preferable to use the word ‘silt size’ and ‘clay size’ in place of simply ‘silt’ or ‘clay’.

As group index is a mean of rating the value of soil as a sub-grade material. It can be used for finding the performance and quality of the soil.

Soil classification of composite soils exclusively based on the particle size distribution is known as textural classification.

The purpose of soil classification is to arrange various types of soils in to groups according to their engineering or agricultural properties.

Since the textural classification is based on the percentages of sand, silt, and clay size making up the soil. Such a classification is more suitable for describing coarse-grained soil.

Triangular classification of U.S. public road administration is a commonly used system for textural classification.

Indian standard classification (IS: 1948-1970) is based on the M.I.T. system.