Dynamic Light Scattering (DLS) measures time dependence of light scattering intensity change. The Stokes-Einstein relation (1) allows us to calculate the hydrodynamic radius Rh (lower limit ~ 0.5 nm and upper limit ~ 500 nm) from the translational diffusion constant Dt. The solvent dynamic viscosity and temperature must be known. Rh depends only on the physical size and size-related behavior (diffusion, viscosity) of the molecule. Information about concentration or refractive index increment is not necessary for a DLS experiment.