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

Group index of soil usually varies by

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

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.

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.

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

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’.

Particle size classification used only as a designation of particle sizes, and do not signify the naturally occurring types which are mixtures of a particle of different sizes.

HRB classification system, also known as public road administration (PRA) is based on both the particle-size composition and plasticity characteristics.

Based on HRB system, the soil is divided into 7 primary groups, designated as A-1, A-2…A-7.