GC Content Calculator for DNA & RNA
Calculate GC%, AT% and per-base composition for DNA or RNA.
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Calculate the GC content, GC percentage, AT content and full base composition of any DNA or RNA sequence. GC content is the fraction of guanine (G) and cytosine (C) bases in a sequence; it influences primer melting temperature, PCR conditions and overall sequence stability, so it is one of the first things to check when designing an experiment. IUPAC codes are handled by what they pin down: S counts toward GC and W toward AT, while codes that could be either pair are excluded from the percentages and reported on their own.
Working on a whole construct rather than one sequence? Open SeqStudio β the full editor, with live feature annotation, plasmid maps, restriction and primer panels, undo/redo, multi-document tabs and GenBank / SnapGene import and export.
How to use the GC Content tool
- 1Paste a DNA or RNA sequence, or a FASTA record.
- 2Read the GC% and AT% along with per-base counts for A, C, G and T/U.
- 3Use the composition to inform primer design, PCR annealing temperatures or quality checks.
Frequently asked questions
How is GC content calculated?
GC content is the number of G and C bases divided by the total number of bases that resolve to one pair or the other, expressed as a percentage: GC% = (G + C + S) / (A + C + G + T/U + S + W) x 100. S and W join the counts because S is always G or C and W is always A or T; codes that span both pairs are left out of the ratio entirely.
What does GC content mean in DNA?
GC content describes how much of a DNA sequence is made of guanine and cytosine bases. Higher GC content usually means stronger base pairing and often a higher melting temperature.
Is GC content the same as GC percentage?
Yes. GC content is usually reported as GC percentage, the percent of bases in a sequence that are G or C.
How are ambiguous bases counted?
By what they actually determine. S means G or C and W means A or T, so S counts toward GC and W counts toward AT even though neither names a specific base. Every other IUPAC code (N, R, Y, K, M, B, D, H, V) spans both a G/C and an A/T base, so it is counted separately and excluded from both totals. All codes are broken out individually in the composition table either way.
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Guides
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