Frequently Asked Questions
Everything you need to know about the GC Content Calculator.
How does the GC content calculator work?
Paste in a DNA or RNA sequence (or FASTA file), and it instantly calculates the percentage of G and C bases along with full base composition.
What is GC content and why does it matter?
It's the proportion of guanine and cytosine bases in a sequence; higher GC content generally means higher thermal stability, which matters for primer design and genome analysis.
Can I paste a FASTA file directly?
Yes, header lines starting with > are automatically stripped, and multiple sequences in one file are analyzed separately.
Does it work with RNA sequences too?
Yes, it auto-detects RNA (uracil) vs DNA (thymine) and calculates GC content accordingly.
What is sliding window analysis?
It calculates GC content across a moving window of the sequence, revealing regions with unusually high or low GC content that a single overall percentage would hide.
How is melting temperature calculated?
Short sequences use the Wallace rule (2°C per A/T, 4°C per G/C); longer sequences use a GC%-based approximation formula, both shown alongside the result.
What if my sequence has ambiguous bases like N?
They're counted and reported separately rather than being silently included in the GC percentage.
Is there a sequence length limit?
No practical limit for typical use; very large genome files may be slow since everything runs in your browser.
Is my sequence data uploaded anywhere?
No; all calculations happen locally in your browser.
Is this tool free?
Completely free, no sign-up or downloads.