Bioinformatics quick tool

GC Content Calculator

Calculate GC percentage, GC count, AT count, and sequence length for nucleotide sequences directly in your browser.

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Browser-side processingFASTA headers ignoredCopy results in one click
What this calculator checks
A fast QC step before notebook analysis, primer review, or sequence comparison.

Counts G and C bases, then calculates the GC percentage from valid bases.

Supports mixed-case input, whitespace, and simple FASTA-style headers.

Flags invalid characters so you can clean the sequence before downstream analysis.

Sequence input
Paste a DNA or RNA sequence. U is treated as a thymine-like base for counting purposes.

Use this as a quick QC step before moving into Runcell notebooks for deeper sequence analysis or protein-focused workflows.

Results
Copy any value directly or review the composition breakdown below.

GC count

18

G + C bases

AT count

15

A + T/U bases

Sequence length

33

Valid bases counted

GC content

54.55%

GC / total valid bases

Composition summary
Per-base breakdown for a quick read on sequence balance.

A

Adenine

7

21.2%

C

Cytosine

8

24.2%

G

Guanine

10

30.3%

T/U

Thymine or uracil

8

24.2%

N

Ambiguous base

0

0.0%

Validation

Sequence looks valid. Whitespace and FASTA headers are ignored.

GC percentage is calculated from the valid bases that remain after trimming whitespace and FASTA headers.

Why GC content matters

A quick QC check before notebook analysis

GC content is one of the simplest sequence quality checks you can run before moving into notebooks, lab notes, or broader sequence analysis. It helps you spot unusual composition, compare related sequences, and sanity-check primer inputs.

High GC
Often associated with stronger binding and higher melting temperatures.
Balanced GC
Useful for quick comparison across related amplicons or constructs.
Low GC
May indicate an AT-rich region that deserves a closer look in context.
Runcell bridge
Carry a QC result into a notebook when you want to compare many sequences, annotate outputs, or document the next step.

GC content is a good first pass. Runcell helps when the work grows into batch comparisons, charting, or protein-related analysis in a notebook.

Explore notebook workflowsOpen reverse complement
Related tools
Stay inside the same sequence-analysis cluster instead of bouncing back to the index.
Reverse Complement

Flip the strand before checking GC content in the other orientation.

Restriction Site Finder

Scan the same sequence for common cloning sites.

DNA Concentration Calculator

Convert lab inputs once the sequence check looks right.

Protein Concentration Calculator

Continue into protein-side planning when the workflow expands.

Next step

Move from a single sequence check to notebook-based analysis.

Compare samples, add charts, and keep the workflow reproducible in Runcell.

Bioinformatics tools hubOpen Runcell

FAQ