The disclosure relates to a method for determining a hydrodynamic size of an object, such as a nano-sized object, said method comprising the steps of: —providing a fluid interface, —linking said object to said fluid interface thereby providing a linked object, whereby the movement of said linked object is restricted by virtue of being linked to said fluid interface, —providing and determining a hydrodynamic shear force that acts on said linked object, —tracking the movement of said linked object, and —calculating the hydrodynamic size of the object using the Einstein-Smoluchowski relation.