Free tool · All tools
GC content calculator
Paste a DNA or RNA sequence and get its GC content, AT content, base-by-base counts, approximate melting temperature and molecular weight — the first numbers you check for primers, probes and gene synthesis.
0 bases · Spaces, line numbers and FASTA headers are removed automatically.
Summary
Good to know
What GC content tells you
GC pairs bind with three hydrogen bonds, so GC-rich sequences melt at higher temperatures and can be harder to amplify in PCR. Most primer designers aim for 40–60% GC; very high GC in a gene can also affect sequencing and synthesis.