GC content is the percentage of nucleotides in a DNA or RNA sequence that are either guanine (G) or cytosine (C). It is calculated as (G + C) / total bases × 100%.

Why does GC content matter?

G-C base pairs form three hydrogen bonds vs. two for A-T pairs, making GC-rich sequences more thermally stable. GC content affects primer melting temperature, cloning efficiency, and organism classification.

Does this tool support RNA sequences?

Yes. RNA sequences use uracil (U) instead of thymine (T). The tool recognizes U and counts it in the AT/AU group automatically.

What characters are accepted?

Only A, T, U, G, and C are counted. Numbers, spaces, and FASTA header lines (starting with >) are ignored. Any other letters are flagged as invalid and excluded from the count.

Is my sequence data sent to a server?

No. All calculation happens locally in your browser using JavaScript. Nothing is transmitted or stored.

What is a typical GC content range?

Human genomes average around 40–41% GC. Bacterial genomes range from about 25% (Mycoplasma) to over 70% (Streptomyces). PCR primers are typically designed to have 40–60% GC content.

GC Content Calculator

Paste a DNA or RNA sequence to instantly calculate GC content percentage and full nucleotide breakdown.

DNA / RNA Sequence

Results

Enter a sequence and click Calculate

GC Content

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AT / AU Content

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Composition

G C A T / U

Nucleotide Breakdown

Base	Count	Percentage

Total Bases

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Sequence Type

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Invalid Characters

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GC Ratio (G:C)

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Summary

The GC Content Calculator analyzes a DNA or RNA nucleotide sequence and reports the percentage of guanine (G) and cytosine (C) bases. GC content is a key metric in molecular biology used to assess primer melting temperature, genome stability, and species identification. This tool runs entirely in your browser — no sequence data is ever transmitted.

How it works

Paste or type your DNA or RNA sequence into the input field.
The tool strips whitespace and converts the sequence to uppercase automatically.
Invalid characters are flagged; only A, T, U, G, C are counted.
Guanine (G) and cytosine (C) bases are summed, then divided by the total valid base count.
Results show GC%, AT/AU%, nucleotide counts, and a visual composition bar.

Use cases

Check GC content of PCR primers to estimate melting temperature (Tm).
Assess genome stability — higher GC content generally means higher Tm.
Quality-check sequences from FASTA files before analysis.
Compare GC content across different organisms or genes.
Validate synthetic gene designs for expression optimization.
Screen sequences for GC-rich secondary structure prone regions.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu