GC Content Calculator

GC Content Calculator

The proportion of guanine (G) and cytosine (C) bases in a DNA sequence - known as GC content - affects everything from DNA stability to PCR primer design.

GC Content% = ((G count + C count) / Total Length) x 100

Example

Sequence: ATGCGCTATAGCGCTA (16 bases, 8 G/C bases)

GC Content = (8 / 16) x 100 = 50.0% (moderate GC content)

Why GC Content Matters

G-C base pairs form three hydrogen bonds, compared to just two for A-T pairs, making GC-rich DNA regions more thermally stable and giving them a higher melting temperature. This directly affects PCR primer design (primers need balanced GC content for reliable annealing), DNA sequencing quality, and even genome organization, since GC content often correlates with gene density in many organisms.

How It Varies Across Life

Human genomic DNA averages around 41% GC content, while bacterial genomes range enormously - from roughly 25% in some AT-rich species up to over 70% in GC-rich species like certain Streptomyces bacteria. This variation reflects deep evolutionary differences in genome composition and mutational biases between lineages.