Letters of Recommendation from faculty

[ginsberg16]

I planned to apply to graduate programs in chemical engineering using a LOR from the professor who I have been working in his lab and two LOR's from the post-docs who I have been working closely in the labs. My friend said that I would need at least 2 or 3 LoR's from faculties. I didn't keep good relationships with other professors or lecturers. And It is too late for me to do that because I am about to graduate. Additionally, due to my average gpa, I would have more chance to get accepted with letters from post-docs because they know me well. What should I do now? Is it true that you need most of your LOR's must be from faculties? (I checked graduate programs's website; some of them don't say it clearly at all :| ) Did anyone here actually use 2 or 3 LOR's for your grad school application without any problem?

Thank you very much! I appreciate all replies

[fuzzylogician]

Generally speaking, faculty will have more experience training students than postdocs do. Therefore, they will have a broader view of their field and a better ability to compare students and to discuss their potential to succeed in grad school. They may also be better known to the readers, and therefore their opinion may count for more. 

That said, it's generally better to get strong letters than letters from more famous people (as long as they at least have a PhD and can discuss someone's potential to succeed in a PhD program with at least some authority). One option you might consider is having the postdoc co-write the letter with the PI, assuming that you were in different labs with different PIs. That way you both get the details and personal touch that the postdoc can provide and the authority that the PI has.