Convert between mass, moles, and copies for dsDNA, ssDNA, ssRNA, and dsRNA. OD₂₆₀ concentration, ligation insert mass, C₁V₁ = C₂V₂ dilution, and qPCR copy-number calculations — all in one tabbed tool. Runs entirely in your browser.
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A 1 kb dsDNA fragment (MW ~649 kDa) has roughly twice the molecular weight of a 1 kb ssDNA (MW ~330 kDa). If you use the wrong type toggle, your moles and copy numbers will be off by ~2-fold.
The 50/33/40 ng/µL per OD₂₆₀ values assume average base composition. GC-rich or AT-rich sequences deviate. For short oligos (<40 nt), use the nearest-neighbor extinction coefficient instead.
A 1:3 insert:vector molar ratio does NOT mean 3× the mass. If your insert is smaller than your vector (which is typical), the mass of insert will be less than 3× the vector mass.
C₁V₁ = C₂V₂ assumes you are diluting (C₂ C₁). If C₂ > C₁, you would need to concentrate — the formula still gives the correct volume, but you cannot simply add diluent to achieve it.
For plasmid copy-number calculations, the result assumes the average 649 Da/bp for dsDNA. If your plasmid has unusual modifications (methylation, etc.), the actual MW may differ slightly.
Standard nucleic acid conversion formulas using MW constants from Sambrook & Russell (Molecular Cloning, 4th ed.): dsDNA 649 Da/bp, ssDNA 330 Da/nt, ssRNA 340 Da/nt, dsRNA 680 Da/bp. Avogadro constant: 6.02214076 mol⁻¹ (2019 SI exact). OD₂₆₀ factors: dsDNA 50, ssDNA 33, ssRNA 40, dsRNA 46 ng/µL per absorbance unit. Ligation formula: insert_ng = (insert_size / vector_size) ratio vector_ng.
Last validated 2026-04-07. Calculations are designed for planning and documentation support; verify procurement decisions against manufacturer specifications or institutional SOPs.
ConductScience DNA / RNA Bio Converter (v1.14.0). ConductScience, Inc. 2026. Available at: https://conductscience.com/tools/dna-rna-bio-converter
Sambrook J, Russell DW. Molecular Cloning: A Laboratory Manual. 4th ed. Cold Spring Harbor Laboratory Press; 2012. doi:10.1101/pdb.top101
NEB. NEBioCalculator. New England Biolabs. 2024. Available at: https://nebiocalculator.neb.com/
The molecular weight of a nucleic acid depends on its length and type. For dsDNA, the average MW per base pair is ~649 Da (counting both strands and the Na⁺ counterion). For ssDNA it is ~330 Da per nucleotide, for ssRNA ~340 Da/nt, and for dsRNA ~680 Da/bp.
To convert between mass and moles:
So 1 ng of a 1,000 bp dsDNA fragment (MW = 649,000 Da) contains about 1.54 fmol or ~9.3 copies.
Nucleic acids absorb UV light at 260 nm due to purine and pyrimidine ring systems. The Beer–Lambert law relates absorbance to concentration: , where is the extinction coefficient, c is concentration, and l is the path length.
The standard convention: 1 OD₂₆₀ unit = 50 ng/µL for dsDNA, 33 ng/µL for ssDNA, 40 ng/µL for ssRNA. These are approximations for "average" base composition. For precise work on known sequences, use the exact extinction coefficient computed from the nucleotide sequence.
For sticky-end ligations, a 1:3 vector:insert molar ratio is the standard starting point. For blunt-end ligations, try 1:5 or 1:10 because blunt-end ligation is less efficient.
The formula insert_ng = (insert_size / vector_size) ratio vector_ng ensures you add the right molar ratio regardless of fragment sizes. If your insert is half the size of your vector, you need half the mass for a 1:1 molar ratio.
