We can use the Define and Edit Binding Site tools.

From the Tools panel: Define and Edit Binding Site > Define Site > From Receptor Cavities. This tool uses a site-finding ‘eraser’ algorithm to detect binding sites – cavities in the protein structure.

After you click the From Receptor Cavities button, a list of Sites are shown in the Hierarchy view. A set of points (green) are displayed in the Molecule window. In the Data Table, three tabs are added: Binding Site, BindingSitePoint, SphereObject.

In the Binding Site tab, see the two columns: Volume, Point Count.

Volume is the volume of each binding site, in cubic angstroms.