DNA / RNA Molecular Weight Calculator
Calculate the molecular weight of an oligonucleotide from its sequence. Choose single-stranded DNA, double-stranded DNA or single-stranded RNA; the calculator sums the residue masses using the standard formulas.
Enter a nucleotide sequence (A, C, G, T/U) to calculate its molecular weight.
How it works
The molecular weight of an oligonucleotide is the sum of the masses of its nucleotide residues, adjusted for the terminal phosphate. For single-stranded DNA the calculator uses the standard per-residue values (A 313.21, T 304.20, C 289.18, G 329.21 g/mol) minus 61.96; single-stranded RNA uses the ribonucleotide values with U in place of T. Double-stranded DNA is the sum of the sense strand and its complement.
Enter a sequence and pick the molecule type. FASTA headers, spaces and numbers are ignored, and the result is shown in g/mol and kilodaltons. These anhydrous values match the figures reported on oligo synthesis specification sheets.
Examples
- ssDNA ACGT = 1173.84 g/mol.
- ssRNA ACGU = 1223.81 g/mol.
- dsDNA is the sum of both complementary strands.
Frequently asked questions
- How is oligo molecular weight calculated?
- By summing the molecular weights of each nucleotide residue and subtracting 61.96 for the removal of the terminal phosphate. Different residue masses are used for DNA and RNA.
- What is the difference between ssDNA and dsDNA weight?
- Single-stranded DNA counts one strand; double-stranded DNA adds the complementary strand, so its molecular weight is roughly twice that of the single strand.
- Why does my synthesis sheet differ slightly?
- Small differences arise from chemical modifications, 5' phosphates or different end chemistries. The calculator uses the standard unmodified anhydrous values.
- Can I use it for RNA?
- Yes. Select ssRNA and the calculator uses ribonucleotide masses, treating T as U so you can paste either alphabet.