The correlation of hydrodynamic radius with protein molecular weight (Mw) is dependent on protein conformation. If proteins are globular, a strong correlation between Rh and Mw is observed. If proteins are unstructured or elongated the measured Rh will be larger than that of a globular protein of identical Mw. Consequently, comparison to a calibration curve of globular proteins will yield a good approximation of Mw for a globular protein of unknown Mw. This principle is used to calibrate SEC columns using samples of known molecular weights as the calibration standards.
To learn how to convert between hydrodynamic radius and molecular weight visit our FAQ on the topic here, we also have a Hydrodynamic Radius Converter to help convert between molecular weight and hydrodynamic radius.