🧬 DNA/RNA Concentration Calculator
Calculate nucleic acid concentration from UV absorbance at 260nm, with an optional A260/A280 purity check.
Frequently asked questions
Why do dsDNA, ssDNA, and RNA use different conversion factors?
The factor converts absorbance at 260nm into concentration, and it depends on how strongly each type of nucleic acid absorbs UV light per unit mass, which differs due to structural differences (double-stranded DNA is more compact due to base stacking, giving it a lower extinction coefficient per unit mass than single-stranded nucleic acids).
What A260/A280 ratio indicates a pure sample?
Approximately 1.8 for pure DNA and approximately 2.0 for pure RNA are the accepted benchmarks. Ratios noticeably below these values often indicate protein or phenol contamination carried over from extraction, while ratios above can sometimes indicate RNA contamination in a DNA prep (or vice versa).
Is A260/A280 enough to confirm sample purity?
Not fully — A260/A280 primarily detects protein and phenol contamination, but doesn't detect other common contaminants like guanidine salts or residual ethanol. Many labs also check the A260/A230 ratio (should be roughly 2.0-2.2) as an additional purity indicator when available from the instrument.
Accuracy & how this is derived
Derivation: Standard Beer-Lambert-derived nucleic acid quantification: concentration equals A260 multiplied by an empirically determined conversion factor (50 for dsDNA, 33 for ssDNA, 40 for RNA, all in microgram/mL per absorbance unit) and any dilution factor applied before measurement.
Validated against: Standard UV spectrophotometric nucleic acid quantification factors used across molecular biology (e.g. as implemented in NanoDrop and similar spectrophotometer software).
⚠️ For educational and research support only — verify critical results independently before use in regulated, clinical, or publication-bound work.
✔ Last updated: July 2026 · Report an error
Quantifying nucleic acids by UV spectrophotometry
Nucleic acid quantification by UV spectrophotometry relies on the predictable relationship between absorbance at 260nm and nucleic acid concentration, using an empirically determined conversion factor that differs for double-stranded DNA, single-stranded DNA, and RNA due to their distinct UV absorption properties. Alongside concentration, the ratio of absorbance at 260nm to 280nm provides a quick purity check, since protein (which absorbs strongly at 280nm due to aromatic amino acids) and other common contaminants shift this ratio away from the expected value for a clean nucleic acid preparation.