Calculate nucleic acid concentration from A260, with purity assessment from A260/A280 and A260/A230 ratios.
Select your nucleic acid type (this sets the extinction coefficient), enter the A260 reading, path length, and dilution factor. The concentration is calculated instantly. Optionally enter A280 and A230 readings to assess sample purity, and total volume to calculate yield.
Nucleic acid concentration from UV absorbance uses the relationship: Concentration = A260 × conversion factor × dilution factor / path length. The conversion factors are empirically determined: 50 µg/mL for dsDNA, 33 µg/mL for ssDNA, and 40 µg/mL for RNA per 1.0 absorbance unit in a 1 cm path length cuvette.
A260/A280 ratio: Pure DNA gives ~1.8, pure RNA gives ~2.0. Ratios significantly below these values indicate protein contamination. Note that pH affects this ratio — measure in slightly basic buffer (TE, pH 8.0) for most consistent results.
A260/A230 ratio: Should be 2.0–2.2 for pure nucleic acids. Low values indicate contamination with organic compounds like phenol, TRIzol, guanidinium salts, or carbohydrates — common carryover from extraction protocols.
NanoDrop note: NanoDrop and similar microvolume spectrophotometers use a 0.1 cm path length (1 mm). Set the path length to 0.1 if entering raw absorbance from a NanoDrop, though most NanoDrop software already reports the normalized concentration.