DNA and RNA quantification
Concentration and purity from A260, with the conversion factor made explicit.
Genomic DNA, plasmid preps, PCR products — anything duplex.
Exactly what the instrument displayed.
A cuvette is 1 cm. A microvolume instrument uses a far shorter path and usually reports the 1 cm equivalent already — if yours shows the raw reading, put the real path here.
Gives the total yield.
Concentration
21 µg/mL · 0.021 mg/mL
Total yield
A260 / A280
~1.8 for clean double-stranded dna
A260 / A230
~2.0 to 2.2 for a clean prep
c = A₂₆₀ ÷ path × factor × dilution- Purity ratios and what shifts them — BioTechniques, 1997
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Absorbance cannot tell nucleic acid from free nucleotides, and it counts DNA in an RNA prep as though it were RNA. Where the distinction matters, a fluorescent assay is specific and stays accurate far lower. The 260/280 ratio also shifts with pH, so read against the same buffer the sample is in.
About this tool
Turn a spectrophotometer reading into a concentration in ng/µL or µg/mL, corrected for the dilution you made and the path length your instrument uses. The factor differs for double-stranded DNA, single-stranded DNA and RNA, so it is a choice rather than a constant. Reports the 260/280 and 260/230 purity ratios and says what a low one means, because concentration alone cannot tell a clean prep from one carrying phenol.
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Science last reviewed .