DNA Molecular Weight Calculator
Calculate molecular weight (Da/kDa) for single-stranded or double-stranded DNA from sequence or length.
What this DNA mol weight calculator does
This tool estimates DNA molecular weight using common oligonucleotide residue masses. You can calculate by entering an exact sequence (best for primers, probes, and short oligos) or by using length plus GC content (useful for plasmids, PCR products, and fragments).
Results are shown in Daltons (Da) and kilodaltons (kDa). If you provide a DNA mass in micrograms, the calculator also returns an estimated amount in pmol and nmol, which is useful for ligation setup, qPCR standards, and normalization workflows.
Why molecular weight matters in DNA workflows
- Primer preparation: Convert from mass to molarity accurately for PCR and sequencing.
- Cloning: Balance insert and vector with molar ratios (for example, 3:1 insert:vector).
- NGS library handling: Normalize libraries by molecule count, not only by concentration.
- Quality control: Sanity-check expected fragment size against measured mass and yields.
How the calculation works
1) Sequence mode
The calculator counts A, T, G, and C and applies average residue masses for DNA oligos: A = 313.21, T = 304.20, G = 329.21, C = 289.18 (g/mol per residue). A terminal correction is used for unphosphorylated strands. Optional 5' phosphate mass can be added.
2) Length mode
If no exact sequence is available, you can estimate weight from length and GC percentage. The base composition is inferred from GC content, then weighted by residue masses. This is ideal for rough planning when sequence-level precision is not required.
ssDNA vs dsDNA in molecular weight calculations
Single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA) have different total molecular weights because dsDNA includes both strands. For dsDNA in sequence mode, this calculator builds the complementary strand and sums both strand masses.
Example use case
Suppose you have a 20-mer primer and 25 µg/mL stock concentration. First, calculate molecular weight from sequence. Then convert to molarity: moles = mass / molecular weight. This lets you move from ng/µL to pmol/µL and prepare exact working dilutions for PCR.
Important notes and limitations
- Values are estimates using average masses and standard end chemistry assumptions.
- Modified bases (biotin, fluorescent dyes, LNA, phosphorothioates) are not included.
- Salt form, hydration, and synthesis/purification details can shift measured mass slightly.
- For publication-grade quantitation, verify with vendor specifications or mass spectrometry data.
Related terms people search
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