How to estimate the physical size of a molecule? I'm reading some chemistry-related papers that employ concepts of droplet evaporation. Since I am no chemist, I am wondering:
How can I estimate the actual size of a molecule, say  succinic acid?
An order of magnitude would suffice. I'm aware of the fact that most molecules can not be approximated by simple assuming that they are spherical.
Evidently, I don't want to do this bottom-up from quantum mechanics. A broad explanation or just a reference would suffice.
 A: I answered a question much like this in my Chemistry finals, and that was a several page essay. You'll excuse me if this answer is a rather shorter!
The definitive way to measure molecular size is X-Ray crystallography. This gives you the structure of the crystal including the positions of all the atoms, so you automatically get the molecule size. This method works for any material that you can crystallise even including huge molecules like DNA and proteins.
In the gas phase the size of molecules can be easily measured for simple molecules using rotational spectroscopy. This gives you the moments of inertia about various axes and from these you can calculate the bond lengths. The method doesn't work for molecules that are too big and complex or (like succinic acid) that aren't easily vaporised, however the bond lengths are pretty constant across most molecules. So once you have bond lengths for simple molecules you can put these into molecules like succinic acid and calculate the size of the molecule that way.
A: The order of magnitude given by Gugg is correct. The molar volume for the succinic acid is 
$V_m=\frac{M}{\rho}=\frac{118.09}{1.59}\frac{cm^3}{mol}=74.27cm^{3}/mol$
where $M$ is the molar mass and $\rho$ the density. From this, you find the volume of the molecule to be 
$V_{molec}=\frac{V_m}{N_A}=1.23\cdot10^{-22}cm^3 $ 
