Convert an A260 reading into DNA concentration and total yield, with an A260/A280 purity check.
A260 measures all UV-absorbing material, not DNA alone — contaminants inflate the reading. For critical work, confirm with a fluorescence assay (e.g. Qubit) and use a blank-corrected A260.
Concentration (ng/µL)
How to use this tool
Use the blank-corrected absorbance at 260 nm from your spectrophotometer.
If you diluted the sample before measuring, enter the factor (1 if undiluted).
The conversion factor depends on strandedness and on DNA versus RNA.
A280 gives the purity ratio; volume converts concentration into total yield.
Formula & worked example
A260 0.5, dilution 10, dsDNA (factor 50): concentration 0.5 × 50 × 10 = 250 ng/µL; in 100 µL that is 25 µg. With A280 0.28, purity is 0.5 / 0.28 ≈ 1.786.
Limitations — read this before you rely on it
UV absorbance is not DNA-specific: RNA, free nucleotides, phenol and other contaminants absorb at 260 nm. Low readings are also noisy — keep A260 in the instrument's reliable range.
Frequently asked questions
About 1.8 for pure dsDNA and about 2.0 for pure RNA. Lower values suggest protein or phenol contamination; much higher values suggest a blank or measurement problem.
The instrument measures the diluted sample. Multiplying back recovers the original stock concentration.
Yes — blank with the same buffer or water the sample is in, or the baseline offset corrupts the reading.
Fluorescence assays are DNA-specific and far more sensitive at low concentrations. A260 is quick and fine for routine, reasonably pure, concentrated samples.
Below roughly A260 0.05, spectrophotometry is unreliable. Concentrate the sample or switch to a fluorescence assay.