DNA / RNA Concentration Calculator (A260)
By Santaji GadepatilinUpdated October 27, 2026
DNA and RNA absorb ultraviolet light at 260 nm, so a spectrophotometer reading gives their concentration directly. The A260/A280 ratio also tells you how pure the sample is. This free DNA / RNA concentration calculator solves for whichever value you leave blank and shows the formula and steps.
How to use the DNA / RNA concentration calculator
Choose the nucleic acid type, enter the A260 and A280 readings and the dilution factor. The concentration and purity ratio are calculated.
DNA / RNA concentration formula
c (µg/mL) = A260 × conversion factor × dilution
Example
dsDNA diluted 1:10 with A260 = 0.45 and A280 = 0.24:
- Concentration = 0.45 × 50 × 10 = 225 µg/mL
- A260/A280 = 1.88 → acceptable purity
Conversion factors
| Nucleic acid | 1 A260 unit equals |
|---|---|
| Double-stranded DNA | 50 µg/mL |
| Single-stranded DNA | 33 µg/mL |
| RNA | 40 µg/mL |
| Oligonucleotides | about 20–33 µg/mL (sequence-dependent) |
Purity ratios
| Ratio | Pure DNA | Pure RNA | Low values suggest |
|---|---|---|---|
| A260/A280 | about 1.8 | about 2.0 | Protein or phenol contamination |
| A260/A230 | 2.0–2.2 | 2.0–2.2 | Salts, guanidine, carbohydrates |
From concentration to copies
Once you know the mass, convert to copy number with the DNA copy number calculator — essential for qPCR standards and cloning.
Other quantification methods
| Method | Advantage |
|---|---|
| UV absorbance (A260) | Fast, no reagents |
| Fluorescent dyes (e.g. dsDNA-specific) | More sensitive, ignores RNA and free nucleotides |
| Gel electrophoresis | Shows size and integrity |
Fluorometric assays are preferred for low concentrations and for next-generation sequencing library preparation.
Micro-volume spectrophotometers
Instruments that measure 1–2 µL drops use short path lengths and automatically normalise to 1 cm. Enter the reading as shown and set the dilution factor to 1 if you did not dilute.
Reliable readings
Spectrophotometers are most accurate for A260 between about 0.1 and 1.0. Dilute concentrated samples and multiply back with the dilution factor.
Frequently asked questions
How do I calculate DNA concentration from A260?
Concentration (µg/mL) = A260 × 50 × dilution factor for double-stranded DNA. Use 40 for RNA and 33 for single-stranded DNA.
What is a good 260/280 ratio?
About 1.8 for pure DNA and about 2.0 for pure RNA. Lower values suggest protein or phenol contamination.
Are µg/mL and ng/µL the same?
Yes, they are equal.
What is a good A260/A280 ratio?
About 1.8 for DNA and 2.0 for RNA.
Is ng/µL the same as µg/mL?
Yes, they are numerically identical.