Osmometry is the study of osmotic pressure, a colligative property that depends on the number of solute particles. For nonassociating solutes it provides the molecular weight if the sample is homogeneous or the number‐average molecular weight if the sample is heterogeneous. In addition, these measurements provide information about the nature of the solution, whether it is ideal or nonideal, and whether self‐association occurs. It is one of the older methods for studying polymer solutions.