What is the GC Content Calculator?
Calculate GC content for DNA or RNA sequences instantly in your browser. Get GC and AT (or AU) percentages, individual base counts, and the AT/GC ratio. Paste raw sequences or FASTA text. Useful for primer design, melting temperature estimates, and sequence QC. Free, private, and no signup.
How to use the GC Content Calculator
- Choose DNA or RNA sequence type.
- Paste your sequence (A, T/U, G, C — whitespace and FASTA headers are ignored).
- Read GC% and AT/AU% in the summary cards.
- Review per-base counts and percentages in the composition table.
- Copy the summary for lab notes or bioinformatics homework.
Common use cases
- Checking GC% before ordering PCR primers
- Comparing base composition between gene fragments
- Quick QC on downloaded FASTA sequences
Frequently asked questions
- What is GC content?
- GC content is the percentage of guanine (G) and cytosine (C) bases in a sequence: (G + C) / total length × 100.
- Why does GC content matter?
- Higher GC content generally increases DNA melting temperature and can affect PCR primer annealing, hybridization, and genome composition studies.
- How is AT content calculated for RNA?
- For RNA, AU content uses adenine (A) and uracil (U) instead of thymine (T).
- Does it support FASTA format?
- Yes. Lines starting with > are treated as headers and removed before analysis.
- Is my sequence uploaded?
- No. All calculations run locally in your browser.
