Calculate molecular weight, extinction coefficient, and concentration conversions for DNA and RNA oligonucleotides using 2026 standards. Supports common modifications and real-time calculations.
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Enter a sequence and click"Calculate MW"
Molecular weight (MW) of an oligonucleotide is the sum of the atomic weights of all atoms in the molecule, typically expressed in Daltons (Da) or grams per mole (g/mol). For a single-stranded DNA oligonucleotide, MW depends on the sequence composition and any chemical modifications. A typical 20-mer DNA primer has a MW of approximately 6,000-6,500 Da.
Knowing the exact MW is essential for converting between mass (µg) and molar (nmol, pmol) concentrations — a critical step when preparing stock solutions from lyophilized oligos. Vendors typically report the amount of synthesized oligo in either OD260 units or nanomoles, and you need MW to convert between these units for accurate experimental concentrations.
The extinction coefficient (ε260) is equally important: it tells you how much UV light at 260 nm the oligo absorbs, allowing you to measure concentration using a spectrophotometer (NanoDrop, etc.). Our calculator uses the nearest-neighbor method for ε260 calculation, which accounts for base stacking interactions and is more accurate than simple base-additive methods.
After calculating MW, use the dilution calculator to prepare stock solutions and working concentrations.
Calculate melting temperature alongside MW for complete primer characterization.
Use the Primer Analyzer when MW should be reviewed together with Tm, GC%, hairpins, dimers, and mismatch effects.
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