I think you will have a difficult time finding a consensus on how to define the radii of different molecules.  You can find X-ray structure of different molecules in the CCDC or in the Crystallography open database and then use free software such as Mercury to allow you to calculate various measurements of different molecules.

Theoretically it is possible to calculate the radius of molecules in any media via abinitio calculations.For instance the command of "volume" yields the radius of molecules in gas phase or solvents media or any other conditions.

 Thank you for all your answers. I am looking for a rough estimate of sizes based on molecular weight. Like of the molecular mass is 5000 Da what would be the radius? or 3000 Da..etc. Knowing that different molecules have different geometry