DNA Concentration Calculator
Calculate DNA, RNA, or oligonucleotide concentration from absorbance and optical path length.
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CalculatorHow to useFormula & methodWorked exampleAbsorbance and concentrationAvoid correcting the path twiceWhat absorbance cannot tell youFrequently asked questionsRelated calculatorsSourcesHow to use this calculator
- Choose the sample type or supply custom molecular weight and extinction coefficient.
- Enter blank-corrected absorbance and the optical path length represented by that reading.
- Enter how much the original sample was diluted before measurement.
Formula and method
For the assumptions behind these results, read the explanation below. You can also explore DNA Copy Number and Ligation.
A worked example
Double-stranded DNA with absorbance 0.2, a 1 cm path, and a tenfold dilution has concentration 0.2 × 50 × 10 = 100 µg/mL, also equal to 100 ng/µL.
Absorbance and concentration
Nucleic acids absorb ultraviolet light, allowing a spectrophotometer to estimate their concentration. For a fixed sample type and path length, the Beer–Lambert relationship connects absorbance to concentration. The common approximate factors at a one-centimeter path are 50 µg/mL for double-stranded DNA, 33 for single-stranded DNA, and 40 for RNA.
These are mass-concentration factors. They are not interchangeable with a molar extinction coefficient. The custom option uses molecular weight and a molar coefficient to calculate a mass concentration with the necessary conversion from grams per liter to micrograms per milliliter.
Avoid correcting the path twice
Some instruments report absorbance already normalized to a one-centimeter path even when the physical measurement uses a much shorter path. In that case, enter 1 cm here. Applying the physical microvolume path to an already normalized result would inflate the calculated concentration. Consult the instrument output definition.
The dilution factor restores the concentration of the original sample. For example, one volume of sample made up to ten total volumes has a factor of ten. An undiluted sample has a factor of one. Absorbance belongs to the measured preparation; the reported original concentration includes the factor.
What absorbance cannot tell you
Other absorbing substances can contribute to the reading. A concentration estimate does not by itself establish DNA purity, fragment integrity, or suitability for a downstream reaction. Appropriate blanking, purity measurements, and a method suitable for the concentration range remain important.
For short or modified oligonucleotides, use sequence-specific properties supplied by the manufacturer or an appropriate sequence model. The custom fields accept those properties; this tool does not infer them from a sequence.
Frequently asked questions
Why are µg/mL and ng/µL numerically equal?
Both numerator and denominator change by a factor of 1,000, so their ratio stays the same.
Can absorbance be zero?
Yes. A zero reading gives a zero estimate. Negative blank-corrected readings are not interpreted as negative concentrations.
Does RNA use the DNA factor?
No. Select RNA so that the 40 µg/mL factor is used instead of the DNA factors.
Sources and further reading
- University of Glasgow — Quantifying DNA: Absorbance to Concentration ↗
Gives the conventional A₂₆₀ conversion factors of 50 µg/mL for double-stranded DNA and 33 µg/mL for single-stranded DNA.
- University of Maryland — Quantifying RNA by Spectral Absorption ↗
Describes A = εCl and the RNA coefficient equivalent to 40 µg/mL per absorbance unit at a 1 cm path.
- University at Buffalo, NESG — Protein Concentration ↗
States the Beer–Lambert equation, molar coefficient units, dilution correction, and the need to handle normalized path length consistently.
- National Institute of Standards and Technology — SI conversion factors ↗
Reference for physical unit conversions. The calculator converts measurements before applying its formula.
Our explanations are written for BiologyCalc. Read how we build and check our tools. These calculations are educational estimates where the underlying model requires assumptions.