DNA Sequence Calculator
Figure out what's really in your DNA sequence. Calculate GC content, melting temperature, molecular weight, and see what makes your sequence tick. Because DNA isn't just code—it's got real physical properties that matter in the lab.
Enter Your DNA Sequence
Enter DNA sequence (A, T, G, C only). FASTA format supported.
Sequence Analysis Results
Sequence Length
0 bp
GC Content
0%
Melting Temp
0°C
Molecular Weight
0 Da
Base Composition
0
Adenine (A)
0
Thymine (T)
0
Guanine (G)
0
Cytosine (C)
AT Content: 0% | GC Content: 0%
Reverse Complement
N/A
This is what the complementary DNA strand would look like if read backwards.
Ready to Analyze Your DNA?
Paste a DNA sequence above (A, T, G, C only) and see what it reveals about your genetic material.
How the DNA Calculator Works (The Math Behind It)
Here's exactly how this calculator crunches the numbers. No magic—just solid molecular biology math.
GC Content Formula
Count guanine and cytosine bases, divide by sequence length, multiply by 100 for percentage.
Melting Temperature (Wallace Rule)
GC pairs get 4°C each, AT pairs get 2°C each. Simple additive formula for basic Tm estimation.
Molecular Weight Calculation
Each nucleotide has its own weight. Subtract 18 Da (water) for each phosphodiester bond between nucleotides.
Reverse Complement
Swap each base with its complement, then reverse the entire sequence. This is how DNA replication works.
Nucleotide Molecular Weights
These include the deoxyribose sugar, phosphate group, and base. Water molecule (18 Da) is subtracted for each phosphodiester bond.
What Do These DNA Calculations Actually Mean?
DNA isn't just a sequence of letters—those A, T, G, and C bases have physical properties that affect how DNA behaves in the real world. Here's what these calculations tell you about your sequence.
GC Content
GC base pairs have three hydrogen bonds (vs. two for AT), making them more stable. High GC content means your DNA is more "sticky" and harder to separate. This affects PCR, sequencing, and how DNA folds.
Melting Temperature (Tm)
The temperature where half your DNA becomes single-stranded. Higher GC content = higher Tm. This is crucial for PCR primer design—you want primers that will anneal at the right temperature.
These aren't just abstract numbers. They determine how your DNA behaves in experiments, how stable it is, and even how it interacts with proteins.
Why GC Content Is a Big Deal in DNA
In PCR Experiments
Primers with very different GC contents won't anneal at the same temperature. Your high-GC primer might not bind while the low-GC one falls off. Aim for 40-60% GC content for reliable PCR.
Rule of thumb: Keep GC content between 40-60% for best PCR results. Too high (>70%) and your primers become finicky. Too low (<30%) and they're unstable.
In Genome Evolution
Different organisms have characteristic GC contents. Humans average ~41%, bacteria like Streptomyces can hit 70%+, and some viruses are under 30%. This affects mutation rates and evolutionary patterns.
Evolution fact: GC-rich genomes are more stable against mutations, but they cost more energy to replicate. It's a biological trade-off.
Practical PCR Tips Based on DNA Calculations
Primer Melting Temps
Good primers have similar Tm values (within 5°C). If one primer's Tm is much higher, it won't anneal properly. Use this calculator to check before ordering primers.
GC Content Balance
Don't design primers that are all GC-rich or all AT-rich. Mix it up! A primer like "GCGCGCGC" will have weird binding properties compared to "ATATATAT".
Template Secondary Structure
High GC regions can form hairpin loops or dimers that screw up PCR. If your template has >80% GC in spots, you might need special enzymes or additives.
Pro PCR Tip
Always design primers with Tm around 55-65°C. Too hot and they won't bind. Too cold and they'll bind nonspecifically everywhere. This calculator helps you hit that sweet spot.
DNA Analysis Questions People Actually Ask
What's a "good" GC content for DNA?
For most applications, 35-65% GC is ideal. Under 30% and your DNA is floppy and unstable. Over 70% and it becomes rigid and hard to work with. Natural DNA averages around 40-50% GC across most organisms.
Why does GC content affect melting temperature?
GC base pairs have three hydrogen bonds vs. two for AT pairs. More bonds = more energy needed to break them apart = higher melting temperature. It's basic chemistry—stronger bonds need more heat.
My primers have different Tm values. Is that bad?
Yes, it's a problem. Primers should anneal at similar temperatures (within 5°C). If one primer's Tm is much higher, you'll get poor amplification or no product at all. Redesign your primers to match.
Can I use this for RNA sequences?
Not directly. RNA uses U instead of T, and the calculations would be slightly different (RNA is generally less stable). Convert U to T first, or use an RNA-specific calculator. The molecular weight would also be different.