The shape of a surfactant molecule can be described by its surfactant packing parameter,  (Israelachvili, 1976). The packing parameter takes into account the volume of the hydrophobic chain (), the equilibrium area per molecule at
the aggregate interface (), and the length of the hydrophobic chain ():
The packing parameter for a specific surfactant is not a constant. It is dependent on various conditions which affect each the volume of the hydrophobic chain, the cross sectional area of the hydrophilic head group, and the length of the hydrophobic chain. Things that can affect these include, but are not limited to, the properties of the solvent, the solvent temperature, and the ionic strength of the solvent.