How to determine the size of gene to amplify? - (Jan/30/2014 )

Hi!

I am going to use PCR to amplify the tetracycline resistance gene from pBR322. I do not know how to determine the size of this gene and therefore I am not sure what size of DNA marker I should use.

Could anyone please explain to me how to determine the size of this gene? Is there any formula or anything like that I could use? 

What I would do is get the sequence of the plasmid and look for open reading frames.  The map for pBR322 should also be available and tell you where this gene is located and the size.