To go from concentration (i.e. molarity) to weight per volume would require you to know the molecular weight. The molecular weight will depend on the sequence of the oligonucleotide. In short, it's not possible to answer your question as it is stated.

However, the additional information you need might be on the synthesis report for the primer (if you have it).

Hi

With Promega BioMath Calculator you can obtain, easy and fast that info. In addition to concentracion (molarity) you have, you will need the number of bases of your primer. 

Here is the link:

http://www.promega.com/a/apps/biomath/index.html?calc=ugpmols

Best!

Thanks for your reply, yes the bases are 38