Mass ↔ Moles ↔ Copies · DNA/RNA

Choose sequence mode or length estimate mode

Use sequence mode when you know the canonical base sequence. The calculator derives a theoretical, composition-specific molar mass and fills the length automatically. Leave the sequence blank and enter a length to obtain a less precise estimate from a fixed average mass per nucleotide or base pair.

Sequence mode
Accepts only A, C, G, and T for DNA or A, C, G, and U for RNA. Linear strands are treated as unmodified and non-5′-phosphorylated. In ds mode, the entered strand is paired with its perfect Watson–Crick complement.
Length estimate mode
Useful for approximate conversions when only nt or bp length is known. Base composition and end chemistry can make the actual molar mass differ, especially for short molecules.
Not modeled
Ambiguous or noncanonical bases, chemical modifications, overhangs, mismatches, counterions, salts, and sample heterogeneity are not included.
No file selected
One single-record FASTA or plain-text file, up to 100,000 canonical bases. Processed locally in your browser.
[bp]Used only when sequence is blank. This is an average-mass estimate; ds length is in bp and ss length is in nt.
▶ Calculated molar mass
g/mol for linear dsDNA
▶ Mass → moles and copy number
copies
▶ Moles → mass and copy number
copies
Avogadro: 6.02214076 × 10²³ mol⁻¹Sequence mode is composition-specific; length mode is an average-mass estimate. Molar mass in g/mol and molecular mass in Da are numerically equivalent.
Related calculators:

How this nucleic acid mass calculator works

This calculator converts between nucleic acid mass, amount of substance (moles), and the number of molecules. It can be used to plan experiments involving primers, PCR products, DNA or RNA oligonucleotides, synthetic gene fragments, and sequencing libraries when the sequence or the length and strandedness are known.

Sequence mode calculates a composition-specific theoretical molar mass based on the nucleotide sequence. Length mode estimates molar mass using fixed average nucleotide masses, providing an approximate value when the sequence is unknown.

Molar-mass models and assumptions

Sequence mode sums base-specific residue masses. A linear strand is modeled as an unmodified, non-5′-phosphorylated oligo with standard 5′ and 3′ hydroxyl termini. Circular mode treats each strand as covalently closed and therefore does not apply the linear terminal correction. For dsDNA or dsRNA, the entered sequence defines one strand and the calculator adds the mass of its perfect Watson–Crick complement.

This standard linear-oligo convention is intended for canonical, unmodified sequences. The IDT OligoAnalyzer supports additional oligo chemistries that this calculator does not. For a modified oligo, use the molecular weight on its specification sheet or a calculator that includes the specific modification.

Length estimate mode does not infer sequence composition. It uses the fixed average values shown below, with the configured linear terminal correction added once per molecule. These are approximations, and the discrepancy can be proportionally larger for short molecules or unusual base composition.

linear length estimate (g/mol) = length × average mass per nt or bp + terminal correction

circular length estimate (g/mol) = length × average mass per nt or bp

linear sequence mode per strand (g/mol) = sum of base-specific residue masses − 63.980 + 2.016

circular sequence mode per strand (g/mol) = sum of base-specific residue masses

dsDNA estimate: 607.4 g/mol per bp + 157.9 g/mol

ssDNA estimate: 303.7 g/mol per nt + 79.0 g/mol

dsRNA estimate: 639.4 g/mol per bp + 157.9 g/mol

ssRNA estimate: 320.5 g/mol per nt + 15.9 g/mol

Core conversions

moles = mass (g) ÷ MW (g/mol)

copies = moles × 6.02214076 × 1023

mass (g) = moles × MW (g/mol)

Worked example

For a 1000 bp linear dsDNA fragment in length estimate mode, the calculated molar mass is 607,558 g/mol. A mass of 1 µg is:

MW = 1000 × 607.4 + 157.9 = 607,557.9 g/mol

moles = 1 × 10-6 g ÷ 607,557.9 g/mol

moles = 1.646 × 10-12 mol = 1.646 pmol

copies = 1.646 × 10-12 × 6.02214076 × 1023

copies = 9.912 × 1011