DNA/RNA GC Content Calculator

Summary

Paste a DNA or RNA sequence (or FASTA) and instantly get GC%, AT%, and per-base counts with a visual composition bar.

How it works

1. Paste a raw sequence or FASTA-format text into the input box.
2. FASTA header lines starting with ">" are automatically removed.
3. Whitespace, digits, and dashes are stripped; the sequence is uppercased.
4. G, C, A, T/U bases are counted; ambiguous IUPAC codes are tallied separately.
5. GC% = (G + C) / (total unambiguous bases) × 100.
6. Results update live as you type, with a visual composition bar and per-base table.

Use cases

• Estimate PCR primer melting temperature — higher GC content raises Tm.
• Assess cloning insert stability before vector ligation.
• Check genome or gene GC bias for phylogenetic comparisons.
• Validate synthesized oligonucleotides against specification sheets.
• Screen promoter regions for GC-rich regulatory motifs.
• Quickly characterize unknown sequences pasted from NCBI BLAST results.
• Identify AT-rich regions prone to melting during stringent hybridization.
• Compare GC content across multiple amplicons in a single session.

Frequently Asked Questions