DNA & RNA Molecular Weight Table
Nucleic-acid molecular weight lets you convert between mass, moles, molarity and copy number. If you only know the length, use the average factors below. If you know the actual sequence, calculate the exact mass from base composition, especially for short primers and RNA oligos.
Average molecular weight by molecule type
| Molecule | Unit | Average mass | Typical use |
|---|---|---|---|
| Double-stranded DNA | base pair (bp) | 650 g/mol per bp | Plasmids, PCR products, genomic fragments |
| Single-stranded DNA | nucleotide (nt) | 330 g/mol per nt | Primers and DNA oligos when sequence is unknown |
| Single-stranded RNA | nucleotide (nt) | 340 g/mol per nt | RNA oligos, guides and transcripts when sequence is unknown |
Exact residue masses
Anhydrous monophosphate residue masses in g/mol. Add the appropriate end correction for a full oligo with terminal hydroxyl groups.
| DNA base | Mass |
|---|---|
| A Adenine | 313.21 |
| C Cytosine | 289.18 |
| G Guanine | 329.21 |
| T Thymine | 304.20 |
| RNA base | Mass |
|---|---|
| A Adenine | 329.21 |
| C Cytosine | 305.18 |
| G Guanine | 345.21 |
| U Uracil | 306.17 |
Common conversion formulas
| Conversion | Formula |
|---|---|
| pmol from ng | pmol = ng x 1000 / MW |
| ng from pmol | ng = pmol x MW / 1000 |
| µM from pmol and volume | µM = pmol / µL |
| nM from pmol and volume | nM = (pmol / µL) x 1000 |
| copy number | copies = moles x 6.022 x 10^23 |
MW is molecular weight in g/mol. Convert ng to grams before calculating moles; the formulas above include the 1000 factor for ng ↔ pmol.
Frequently asked questions
- What is the molecular weight of double-stranded DNA?
- A useful average is 650 g/mol per base pair. For example, a 1,000 bp dsDNA fragment is about 650,000 g/mol, or 650 kDa.
- What is the molecular weight of an oligo?
- For a rough estimate, use about 330 g/mol per nucleotide for ssDNA and 340 g/mol per nucleotide for ssRNA. For short oligos, exact base composition matters, so calculate from the sequence when possible.
- How do I convert ng to pmol?
- Use pmol = ng x 1000 / molecular weight, where molecular weight is in g/mol. The molecular weight can come from the length-based average or from the exact sequence.
- Is pmol/µL the same as nM?
- No. One pmol per microlitre equals one micromolar (µM), which is 1000 nM. To get nM from pmol and µL, divide pmol by volume in µL and multiply by 1000.
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Related tools and references
Use these related pages when this table raises a practical calculation or workflow question.