# Topics - HETP

**Height Equivalent to the Theoretical Plate**. It arises from the

**Plate Theory**and is numerically equal to the column length divided by the number of theoretical plates in the column (and in practice is measured in this way). As the HETP is a function of both the properties of the column and the solute, it will vary from one column to another and, more importantly, between different solutes eluted from the same column in the same chromatogram. The HETP is the theoretical link between the Plate Theory and the

**Rate Theory**as the HETP is numerically equal to the

**variance per unit length**of the column as determined from the Rate Theory. The more efficient the column the more theoretical plates in the column the better the resolution and the smaller the HETP. The rate theory provides an equation for the HETP in terms of the physical properties of the solute and phase system, the operating temperature and the mobile phase velocity.