DNA Concentration Calculator
Calculate DNA, ssDNA or RNA concentration from A260 absorbance using Beer-Lambert Law. Enter your spectrophotometer reading and get concentration in ug/mL and ng/uL instantly, plus a 260/280 purity ratio interpretation.
DNA Concentration Calculator Tool
DNA concentration calculator with purity ratio — dsDNA, ssDNA and RNA
Most spectrophotometry calculators handle only dsDNA with a fixed conversion factor. This tool covers dsDNA, ssDNA and RNA with the correct factor for each, adds the 260/280 purity ratio with a plain-language interpretation, and shows results in both ug/mL and ng/uL simultaneously.
How to calculate DNA concentration from A260 absorbance
DNA and RNA conversion factors and purity ratios
| Sample type | CF (ug/mL per A260) | Ideal 260/280 | Notes |
|---|---|---|---|
| dsDNA | 50 | ~1.8 | Standard genomic DNA, plasmid |
| ssDNA | 33 | ~1.8 | Oligonucleotides, primers |
| RNA | 40 | ~2.0 | Total RNA, mRNA, rRNA |
LazyTools DNA Concentration Calculator vs the competition
| Feature | LazyTools | Omni | Thermo NanoDrop | AAT Bioquest |
|---|---|---|---|---|
| dsDNA quantification | ✓ Yes | ✓ Yes | ✓ Yes | ✓ Yes |
| ssDNA quantification | ✓ Yes | ✓ Yes | ✓ Yes | ✓ Yes |
| RNA quantification | ✓ Yes | ✓ Yes | ✓ Yes | ✓ Yes |
| 260/280 purity ratio | ✓ Yes | ✗ No | ✓ Yes | ~ Basic |
| Purity plain-language note | ✓ Yes | ✗ No | ✗ No | ✗ No |
| ng/µL and µg/mL output | ✓ Yes | ✗ µg/mL only | ✓ Yes | ~ Partial |
| Adjustable pathlength | ✓ Yes | ✓ Yes | ✗ Fixed | ✗ No |
| No login required | ✓ Yes | ✓ Yes | ✗ Login | ✓ Yes |
DNA Concentration from A260 — A Complete Guide
DNA quantification by UV spectrophotometry is the fastest and most common method for determining nucleic acid concentration before downstream experiments. It is based on the Beer-Lambert Law: absorbance is proportional to concentration and pathlength.
How to calculate DNA concentration from A260 absorbance
The formula is: C (ug/mL) = (A260 / pathlength) x conversion factor x dilution factor. The conversion factor accounts for the different absorbance per unit concentration between sample types: 50 ug/mL for dsDNA, 33 ug/mL for ssDNA, and 40 ug/mL for RNA. An A260 reading of 1.0 in a 1 cm cuvette with no dilution gives 50 ug/mL dsDNA, or equivalently 50 ng/uL.
Why 260 nm is used for DNA measurement
Nucleotide bases contain aromatic ring structures that absorb UV light strongly at 260 nm. This is the maximum absorbance wavelength for both DNA and RNA. Proteins absorb strongly at 280 nm, which is why the 260/280 ratio is used as a purity indicator.
Understanding the A260/A280 purity ratio
The 260/280 ratio compares nucleic acid absorbance to protein absorbance. For pure dsDNA, the ratio should be approximately 1.8; for pure RNA, approximately 2.0. A ratio below 1.7 suggests protein or phenol contamination. A ratio above 2.1 in a DNA sample may indicate RNA contamination. Note that pH affects this ratio — always measure in a slightly basic buffer (e.g. 10 mM Tris pH 7.5-8.5).
Limitations of the A260 method
The A260 method cannot distinguish intact from degraded DNA, DNA from RNA in the same sample, or nucleic acids from other UV-absorbing contaminants such as free nucleotides. For applications requiring high accuracy at low concentrations (below 2 ng/uL), fluorescence-based methods such as the Qubit assay are more sensitive and specific.