Enter your Absorbance at 260 nm, Dilution Factor, Path Length, DNA Type, and DNA Length into the DNA Concentration Calculator to find your sample's DNA Concentration in ng/µl and molar concentration, plus the A260/A280 Ratio to check your sample's purity.
DNA Concentration
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Concentration (ng/µl)
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Molar Concentration
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A260/A280 Ratio
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For double-stranded DNA, the extinction coefficient is 50 µg/ml per A260 unit. For single-stranded DNA and RNA, it's 33 µg/ml and 40 µg/ml respectively.
DNA has maximum absorbance at 260nm due to the aromatic bases (adenine, thymine, guanine, cytosine). This wavelength provides the most accurate measurement for nucleic acid concentration.
Pure DNA has an A260/A280 ratio of ~1.8. Lower ratios indicate protein contamination, while higher ratios may suggest RNA contamination or degraded DNA.
The dilution factor accounts for any sample dilution before measurement. If you diluted your sample 1:10, the dilution factor is 10, and the calculator multiplies the result accordingly.
Standard spectrophotometer cuvettes have a 1 cm path length. Some microvolume devices use shorter path lengths (0.2-0.5 cm), which should be entered for accurate calculations.
Yes, select RNA from the DNA type dropdown. RNA uses a different extinction coefficient (40 µg/ml per A260 unit) for accurate concentration determination.
Absorbance readings between 0.1-1.0 are most accurate. If your reading is too high, dilute the sample. If too low, concentrate the sample or use a longer path length cuvette.
1 µg/ml = 1000 ng/µl. For molar concentrations, you need the DNA length in base pairs. The calculator provides conversions between µg/ml, ng/µl, and nanomolar concentrations.