GC Content Calculator
Paste a DNA or RNA sequence to get its GC content, AT content and base composition. FASTA headers, spaces and numbers are ignored, and U is counted as T.
Paste a sequence above to see its GC content.
How it works
GC content is the fraction of bases in a nucleic acid that are either guanine (G) or cytosine (C), expressed as a percentage: GC% = (G + C) ÷ (A + T + G + C) × 100. Because G–C base pairs are held together by three hydrogen bonds rather than two, GC content correlates with the melting temperature and stability of the sequence.
Paste a sequence and the calculator reports the GC percentage, the complementary AT percentage, the length, and the count of each base. FASTA headers, line breaks, spaces and numbers are stripped automatically, and uracil (U) in RNA is counted together with thymine (T).
Examples
- GGCC → GC content 100%.
- ATGC → GC content 50%, AT content 50%.
- A 60% GC region melts at a higher temperature than a 40% GC region of the same length.
Frequently asked questions
- What is GC content?
- GC content is the percentage of a sequence made up of guanine and cytosine. It is calculated as (G + C) divided by the total number of bases, times 100.
- Why does GC content matter?
- G–C pairs have three hydrogen bonds versus two for A–T, so higher GC content raises the melting temperature and stability of DNA. It also affects PCR primer design and reflects genome characteristics.
- Does it work for RNA?
- Yes. Uracil (U) is counted as thymine (T), so RNA sequences give the expected GC content.
- What input can I paste?
- Plain sequence or FASTA. Lines starting with > are ignored and whitespace and numbers are removed, so pasting directly from a FASTA file works.