DNA Molecular Weight Calculator
Calculate theoretical molecular mass from an unmodified DNA or RNA sequence, or estimate it from length. Choose strand type, topology and terminal chemistry explicitly, then inspect the base-by-base arithmetic and mass-to-mole conversions.
Enter your values or load an example to see the answer and worked steps. Calculations run in your browser.
Choose sequence or length
Sequence mode counts each nucleotide. For dsDNA it also counts the complementary strand. Length-only mode assumes equal proportions of the four bases, so it estimates mass rather than discovering the composition of your molecule.
Account for ends and circular molecules
The calculation starts with average monophosphate nucleotide masses and subtracts one water molecule for each phosphodiester bond. A linear strand has n − 1 bonds; a circular strand has n. A free 5′-OH removes an additional 79.9799 g/mol from each linear strand relative to a 5′-phosphate.
Read the concentration conversions
For molecular mass M in g/mol, µg/nmol equals M/1,000 and pmol/µg equals 1,000,000/M. These are conversion factors, not the concentration of an unknown sample. Combine them with your measured mass and solution volume separately.
Keep the chemical assumptions visible
RNA here means single-stranded RNA. Labels, counterions, modifications, salts and hydration are excluded. Use the supplier’s molecular mass for a modified oligonucleotide. Average atomic masses differ from monoisotopic masses used in some mass-spectrometry calculations.
References
Related free tools
Frequently Asked Questions
Is a length-only result exact?
No. Base composition affects mass. Length mode assumes equal proportions and labels the answer as an estimate.
What sequence can I paste?
Enter A, C, G and T for DNA, or A, C, G and U for RNA. Whitespace is ignored; FASTA headers, N bases and modifications are rejected.
Which ends are assumed for double-stranded DNA?
Both linear strands use your selected 5′ end chemistry and ordinary 3′-OH ends. Mixed terminal chemistry is not supported.
Why does circular DNA have a different mass?
A closed circle has an additional phosphodiester bond per strand and no free terminal groups. The terminal selector is ignored in circular mode.
Continue in the app
Use Biology AI: Bionomy for the full guided result after this quick check.
