GC Content Calculator
Compute the percentage of G and C bases in a DNA sequence, plus each base count and the total length.
GC content is the share of bases in a DNA sequence that are guanine or cytosine. It matters because G-C pairs bond more tightly than A-T pairs, so a higher GC percentage generally means a more stable, higher-melting strand. For GGCCAT, four of six bases are G or C, so GC content is 66.7%.
GC content
66.7%
Length
6bp
G + C count
4
A
1
C
2
G
2
T
1
How it works
GC content is the fraction of a DNA sequence made up of guanine (G) and cytosine (C) bases, written as a percentage of the total length.
The tool counts each of the four bases, adds the G and C counts, and divides by the sequence length. For GGCCAT, that's four G-or-C bases out of six, which is 66.7%.
It matters because G and C pair with three hydrogen bonds versus two for A and T, so GC-rich stretches are more stable and melt at higher temperatures — useful when designing primers or reading a genome.
Frequently asked questions
Why does GC content affect melting temperature?
G-C pairs are held together by three hydrogen bonds while A-T pairs have only two. More G and C means more bonds to break, so a GC-rich sequence needs more heat to separate its strands.
Does the tool count U from RNA?
No, it works on DNA and accepts only A, C, G and T. If you have an RNA sequence, convert U back to T first, since GC content counts G and C either way.
Is GC content the same as G content plus C content separately?
Yes — it's simply the combined share of G and C bases. The tool also lists each base on its own so you can see how the two split.