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Nucleic Acid Concentration from UV Absorbance

Convert absorbance at 260 nm into approximate nucleic acid mass concentration, with path length, dilution and a custom molecular-weight coefficient.

  • Formula & worked example
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

Double-stranded DNA with A260 0.5, a 1 cm path and a tenfold dilution corresponds to 250 µg/mL in the original sample.

Concentration = absorbance × conversion factor × dilution / path(cm); custom factor = molecular weight / molar extinction coefficient.

Worked example

Enter these known values and leave the other values blank.

Sample type
Double-stranded DNA
Absorbance at λmax
.5
Pathlength
1 cm
Dilution factor
10
Conversion factor
50 μg/mL
Concentration
250 µg/mL

Assumptions and limitations

  • Use blank-corrected absorbance at 260 nm and the optical path in centimeters. A value already normalized to a 1 cm path must use 1 cm here.
  • The captured approximate factors are 33 µg/mL for ssDNA, 50 for dsDNA and 40 for RNA at A260=1 and a 1 cm path. Sequence and contaminants change the true relationship; this is not a purity test.
  • For a custom oligonucleotide use molecular weight in g/mol and extinction coefficient in L/(mol·cm); their ratio is numerically a µg/mL conversion factor.
  • The captured model requires positive absorbance, concentration, path and dilution factor. A factor below one denotes concentration rather than dilution; the note remains visible.

Common questions

How should I solve for another quantity?

Clear the unknown field and enter the independent measurements. A supported inverse preserves the same model; it does not add experimental evidence.

References

The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.

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