Calculate the GC content of a DNA or RNA sequence — the percentage of guanine and cytosine bases. Paste your sequence to get the GC%, AT%, length and base counts instantly.
Enter a sequence to see its GC content.
Counts A, C, G, T and U; other characters are ignored. Calculation runs in your browser.
What GC content is and why it matters
GC content is the fraction of bases that are G or C. Because G–C pairs have three hydrogen bonds versus two for A–T, GC-rich sequences are more thermally stable:
- Melting temperature: higher GC raises the Tm — see the Tm calculator.
- Primer design: aim for 40–60% GC for balanced, specific primers (guide).
- PCR difficulty: very high-GC templates need additives (DMSO, betaine) and higher denaturation.
- Genomics: GC content varies between organisms and across a genome (isochores), and affects sequencing coverage.
How to use it
- Paste a DNA or RNA sequence (FASTA or raw).
- Read the GC%, along with AT%, total length and the count of each base.
Frequently asked questions
How is GC content calculated?
GC% = (G + C) / total bases × 100. Enter a sequence above and it’s computed for you.
What is a good GC content for primers?
Around 40–60% for most applications — enough stability without being hard to denature.
Does higher GC mean a higher melting temperature?
Yes — G–C pairs are more stable than A–T, so GC-rich sequences melt at higher temperatures.
Related guide: How to design PCR primers →
