DNA Concentration Calculator
Calculate DNA concentration from A260 absorbance via Beer-Lambert law. Free spectrophotometry calculator with dsDNA, ssDNA, RNA factors and purity ratio.
About This Calculator
The DNA Concentration Calculator determines the concentration of nucleic acids in your sample using absorbance readings from a UV spectrophotometer. It is an essential tool for molecular biologists, biochemists, and lab researchers who need to quantify DNA or RNA before downstream applications such as PCR, sequencing, restriction digestion, or cloning.
The calculator uses the Beer-Lambert law adapted for nucleic acid quantification. The fundamental formula is: Concentration (µg/mL) = (A260 / pathlength) × conversion factor × dilution factor. The conversion factor depends on the sample type: 50 µg/mL per OD unit for double-stranded DNA (dsDNA), 33 µg/mL for single-stranded DNA (ssDNA), and 40 µg/mL for RNA. These factors are derived from the molar extinction coefficients of nucleotides and have been standardized in molecular biology protocols.
For accurate results, ensure your spectrophotometer is properly blanked and the sample is free of significant contaminants. The A260 reading should be within the linear range of the instrument (typically 0.1–2.0 OD). If your sample was diluted prior to measurement, enter the dilution factor to obtain the original sample concentration.
The calculator also provides the A260/A280 purity ratio when you enter the A280 absorbance. This ratio is a critical quality indicator: pure DNA typically has a ratio of ~1.8, while pure RNA has a ratio of ~2.0. Significant deviations suggest contamination by proteins (lower ratio) or residual organic compounds (ratio above 2.0). Additionally, entering the sample volume allows calculation of total DNA yield, which is useful for assessing extraction efficiency.
Regional Notes
India: Indian research institutions and biotech labs use the same spectrophotometric methods standardized globally. The conversion factors (50/33/40 µg/mL per OD) are universally accepted and do not vary by region.
United States: US laboratories follow the same protocols established by molecular biology standards. The A260/A280 ratio of ~1.8 for pure DNA is universally referenced in US research publications and clinical lab guidelines.
United Kingdom: UK research councils and universities adhere to the same nucleic acid quantification standards. The Beer-Lambert law and conversion factors used here align with protocols from the UK's Medical Research Council (MRC) and Biotechnology and Biological Sciences Research Council (BBSRC).
Frequently Asked Questions
How do you calculate DNA concentration from A260?
DNA concentration is calculated using the formula: concentration = (A260 / pathlength) × conversion factor × dilution factor. For dsDNA the conversion factor is 50 µg/mL per OD, for ssDNA it is 33 µg/mL, and for RNA it is 40 µg/mL.
What is a good DNA concentration for sequencing?
A good DNA concentration for sequencing typically ranges from 10 to 300 ng/µL depending on the sequencing platform and library preparation method. PCR products generally need less concentration than plasmids.
What does the A260/A280 ratio mean for DNA purity?
The A260/A280 ratio is a measure of nucleic acid purity. For pure DNA the accepted ratio is approximately 1.8, while for pure RNA it is approximately 2.0. Lower ratios indicate protein or phenol contamination.
Why is 260 nm used for DNA quantification?
Nucleic acids absorb UV light maximally at 260 nm due to the aromatic bases in DNA and RNA. At 280 nm the absorbance is approximately half that value, which allows the 260/280 ratio to detect protein contamination.
What is the Beer-Lambert law for DNA concentration?
The Beer-Lambert law states that absorbance A = ε × c × l, where ε is the molar extinction coefficient, c is concentration, and l is pathlength. For DNA quantification at 260 nm, the standard conversion factor approach simplifies this to c = A260 × CF / l, using known conversion factors (50 µg/mL for dsDNA per OD).
How do I calculate DNA yield from concentration?
DNA yield is calculated by multiplying the concentration (in µg/mL) by the sample volume (in mL). For example, 50 µL of a 100 µg/mL DNA solution yields 5 µg of total DNA.
What is the difference between dsDNA, ssDNA, and RNA conversion factors?
dsDNA has a conversion factor of 50 µg/mL per OD because double-stranded DNA absorbs less UV light per unit mass. ssDNA uses 33 µg/mL due to its different structure and hypochromicity. RNA uses 40 µg/mL, reflecting its unique base composition and single-stranded nature.
Can I use this calculator for oligonucleotide concentration?
This calculator uses the standard conversion factor method suitable for genomic DNA and RNA samples. For short oligonucleotides, the exact extinction coefficient from the nearest-neighbor model should be used instead of generic conversion factors.