DNA and RNA experiments often require a swift bridge between measured mass, mole amount, and molecule count. This calculator is ideal for PCR templates, PCR primers, DNA and RNA oligos, synthetic fragments, NGS library preparation, ligation, enzymatic reactions, enzyme kinetics, Gibson assembly or NEBuilder assembly tools and other workflows where the molecule length is known but a sequence-specific molecular weight is unnecessary. However, if the exact nucleic acid sequence is known, it can be entered to provide a more accurate estimation.
The calculator estimates molecular weight from length using a linear, end-corrected model. For circular molecules, the terminal correction is omitted because there are no free ends. If you enter a sequence, the calculator uses the base composition of that sequence instead of the length-only constants.
linear MW (g/mol) = length × base weight + terminal correction
circular MW (g/mol) = length × base weight
sequence mode MW = sum of base-specific residue weights - water lost during bond formation
dsDNA: 607.4 per bp + 157.9 terminal correction
ssDNA: 303.7 per nt + 79.0 terminal correction
dsRNA: 639.4 per bp + 157.9 terminal correction
ssRNA: 320.5 per nt + 15.9 terminal correction
moles = mass (g) ÷ MW (g/mol)
copies = moles × 6.02214076 × 1023
mass (g) = moles × MW (g/mol)
For a 1000 bp dsDNA fragment, the estimated molecular weight 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