GC content calculator for DNA and RNA
Paste a DNA or RNA sequence and Aaron's Archive reports its GC content at once: the percentage of bases that are G or C, with the count of every base, the AT content, the purine and pyrimidine share, a sliding-window GC plot and GC skew. It is free, needs no account, and works for a primer, a gene or a whole contig.
GC content matters because a G–C pair has three hydrogen bonds and an A–T pair has two. GC-rich DNA is harder to melt, which changes how PCR, sequencing and primer design behave.
What you get
- GC % and AT % of the whole sequence, with the count of each base
- Purine and pyrimidine percentages
- A sliding-window GC plot, to see where a sequence turns GC-rich or AT-rich
- GC skew and cumulative GC skew, which in bacterial genomes can point to the origin and terminus of replication
- The melting temperature, open reading frames, CpG islands and restriction sites for the same paste
How to use it
- Open the Single tab and paste DNA or RNA, as plain sequence or FASTA.
- Leave the type on Auto, or choose DNA or RNA.
- Press Run analysis and read the GC value and the window plot.
Worked example
Paste this 76-base sequence:
ATGGCTAAGCTTGAATTCGGATCCGCTAGCTGACTGATCGTAGCTAGGCTAAGCTTGGATCCAAGCTAGCTAATAAThe tool counts A 21, T 20, G 19 and C 16. GC content is (19 + 16) ÷ 76 = 46.05% and AT content is 53.95%. A shorter check: ATGCGC has 4 G or C in 6 bases, so 66.67%.
Limits to know about
- If you paste several FASTA records only the first is analysed; the Batch tab analyses all of them.
- Characters that are not part of a sequence are ignored and listed in a warning.
Common questions
How is GC content calculated?
It is the number of G and C bases divided by the sequence length, times 100. The GC content guide shows the formula with a worked example.
What is a normal GC content?
It depends on the organism: about 41% for human DNA and about 51% for E. coli, and 40–60% is the usual target for a PCR primer. The guide has a table of typical values.
Can I use an RNA sequence?
Yes. U is counted in place of T and GC content is worked out the same way.
Are my sequences stored?
No. Sequences are processed in memory to produce your result and are not stored or logged. The privacy policy has the details, including what BLAST sends to NCBI and EMBL-EBI.