GC Content Calculator
Get GC content, AT content, length, ambiguous base count and skew statistics for each sequence in a FASTA file.
What is GC content?
GC content is the percentage of guanine and cytosine bases in a sequence. Because G–C pairs share three hydrogen bonds while A–T pairs share two, GC-rich DNA is more thermally stable. GC content is used to estimate melting temperature, predict PCR success and characterise genomes — bacterial genomes typically sit between 20% and 80% GC.
Other metrics reported
- Length — number of bases in the record.
- N count — ambiguous bases, usually assembly gaps.
- GC skew — (G−C)/(G+C), used to locate origins of replication.
- AT skew — (A−T)/(A+T), same idea for the other pair.
Frequently asked questions
Does it handle RNA?
Yes — U is counted the same way as T for the AT statistic.
Can I analyse a whole genome?
Yes, as long as the pasted text stays under the input limit. For multi-FASTA files each record is reported separately.