GC content

The guanine-cytosine (GC) content of a gene or whole genome is the percentage of nitrogenous bases that are guanine (G) or cytosine (C)

GC content = (number of G's + C's) / (number of T's + A's) * 100

Python: calculate GC content using Bio.SeqUtils

Web calculator: Oligo Calc

http://en.wikipedia.org/wiki/GC-content