DNA Molecular Weight Calculator
Calculate the molecular weight of a DNA molecule from its length and strandedness.
About DNA Molecular Weight Calculator
A single nucleotide averages 330 daltons, so a double-stranded base pair is about 650. Converting nanograms to picomoles requires the molecular weight, which is why the same mass of a short primer contains far more molecules than of a long plasmid. Molar rather than mass equivalence matters in ligation and PCR, so this conversion is needed for every reaction setup.
Formula
DNA Molecular Weight
Double stranded: MW ≈ 650 × bp; single stranded: MW ≈ 330 × bases + 79
- 330 Da
- Average mass of a single nucleotide
- pmol
- Picomoles, the practical unit for oligonucleotide quantities
Worked example
With the default values below, DNA Molecular Weight Calculator returns Molecular Weight of 13,000.00. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Length in bases or base pairsminimum 0
- 20
- Strandednessone of Single stranded, Double stranded
- Double stranded
- Quantity availableminimum 0 ng
- 100 ng
Results
- Molecular Weight
- 13,000.00 Da
- Amount
- 7.69231 pmol
- Number of Molecules
- 4,632,415,969,231
- Mass per Picomole
- 13.00000 ng
- Conversion Factor
- 13.00000 ng/pmol
Step by step
- 1Values used
- 2DNA Molecular Weight
- 3Molecular Weight= 13,000.00 Da
- 4Amount= 7.69231 pmol
- 5Number of Molecules= 4,632,415,969,231
- 6Mass per Picomole= 13.00000 ng
- 7Conversion Factor= 13.00000 ng/pmol
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 5 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is DNA Molecular Weight calculated?
Double stranded: MW ≈ 650 × bp; single stranded: MW ≈ 330 × bases + 79 A single nucleotide averages 330 daltons, so a double-stranded base pair is about 650. Converting nanograms to picomoles requires the molecular weight, which is why the same mass of a short primer contains far more molecules than of a long plasmid.
Why does DNA Molecular Weight matter?
Molar rather than mass equivalence matters in ligation and PCR, so this conversion is needed for every reaction setup.
What values do I need to enter?
This calculator takes 3 inputs: Length in bases or base pairs, Strandedness, Quantity available. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.