DNA Concentration from A260 with Dilution and Purity Ratios
What this DNA concentration calculator does
This calculator estimates DNA/RNA concentration from a spectrophotometer reading at 260 nm (A260). It also computes two common purity ratios (A260/A280 and A260/A230) and estimates total yield based on your sample volume.
Inputs you need
A260, A280, and A230
A260 is used for concentration. A280 and A230 are used for purity ratios: A260/A280 is often used to check protein contamination, and A260/A230 can indicate contamination from salts or organic compounds.
Nucleic acid type
Different nucleic acids use different standard conversion factors (at 1 cm path length). The calculator supports dsDNA, ssDNA, and RNA.
Dilution factor and path length
If you diluted the sample before measuring, concentration should be multiplied by the dilution factor. If the optical path length is not 1 cm, the estimate is adjusted accordingly.
Formulas used
Concentration from A260
The standard approach is: \[ C_{\mu g/mL} = \frac{A_{260} \times F \times D}{L} \] Where: - \(A_{260}\) is the absorbance at 260 nm - \(F\) is the conversion factor (depends on dsDNA/ssDNA/RNA) - \(D\) is the dilution factor - \(L\) is path length in cm Because \(1 \ \mu g/mL = 1 \ ng/\mu L\), the same numeric value can be displayed in either unit: \[ C_{ng/\mu L} = C_{\mu g/mL} \] If you choose ng/mL, the conversion is: \[ C_{ng/mL} = 1000 \times C_{ng/\mu L} \]
Total yield (mass) from concentration and volume
If concentration is in ng/µL and volume is in µL: \[ m_{ng} = C_{ng/\mu L} \times V_{\mu L} \] And in micrograms: \[ m_{\mu g} = \frac{m_{ng}}{1000} \]
Purity ratios
A260/A280
\[ R_{260/280} = \frac{A_{260}}{A_{280}} \] Typical values depend on the nucleic acid type, so the calculator evaluates the ratio using a type-appropriate reference range.
A260/A230
\[ R_{260/230} = \frac{A_{260}}{A_{230}} \] Values around 2.0 to 2.2 are commonly considered “clean” in many workflows, while lower values can indicate contaminants that absorb around 230 nm.
How to interpret the results
Concentration
Use the concentration output to plan downstream steps (PCR, cloning, library prep), adjusting volumes to reach your target mass.
Purity status
The status message is a practical summary based on how far the ratios are from typical ranges. If ratios are strongly off-range, it may be worth re-cleaning the sample or re-measuring with a fresh blank.
Practical tips
- Always verify the correct blank/buffer was used before measurement. - If A260 is extremely low, purity ratios can become unstable. - If your instrument already normalizes to 1 cm, keep path length at 1 cm.