Nucleotide Molecular Weight Calculator
Calculate the molecular weight (MW) of DNA and RNA oligonucleotides instantly. Supports single-stranded and double-stranded formats, 5' phosphorylation, and mass-to-molar conversions.
Molecular weight calculations are estimates based on standard nucleotide masses. Always verify specifications with your oligo manufacturer.
ℹ️ Frequently Asked Questions
What is the molecular weight of a DNA oligo?
The molecular weight depends on sequence length and base composition. This calculator sums individual nucleotide masses and adjusts for terminal chemistry (loss of water during phosphodiester bond formation, plus any 5' phosphate modification).
How do I convert μg to nmol for an oligo?
Use the formula:
nmol = (μg × 1000) / MW
Where MW is the molecular weight in g/mol (Da). This calculator performs this conversion automatically.
Does this calculator support RNA?
Yes. Switch to RNA mode and the calculator will use ribonucleotide masses (with U instead of T) and include the additional hydroxyl group mass at the 2' position.
How is double-stranded DNA MW calculated?
For a self-complementary or paired oligo:
MW(ds) ≈ 2 × MW(single strand)
This is an approximation. For precise dsDNA MW, both strands should be calculated individually.
Does 5' phosphorylation affect molecular weight?
Yes. Adding a 5' phosphate group increases the molecular weight by approximately 79.98 Da. This is common for ligation-ready oligos and some qPCR probes.
How is the extinction coefficient calculated?
The molar extinction coefficient (ε₂₆₀) is estimated using the nearest-neighbor method for single-stranded oligos. For a quick approximation, individual base contributions are summed:
ε₂₆₀ ≈ Σ(base × individual ε)
DNA: A=15400, T=8700, G=11500, C=7400 L/(mol·cm)
RNA: A=15400, U=9900, G=11500, C=7200 L/(mol·cm)