DNA concentration calculator form
This calculator estimates DNA concentration from absorbance, dilution, optical path length, and sample type. It also reports purity ratios, total yield, and dilution-to-target volume.
Formula used
- Concentration (ng/µL) = (A260 × conversion factor × dilution factor) ÷ path length in cm
- Path length in cm = path length in mm ÷ 10
- Total yield (µg) = concentration (ng/µL) × total solution volume (µL) ÷ 1000
- A260/A280 ratio = A260 ÷ A280
- A260/A230 ratio = A260 ÷ A230
- Normalization volume (µL) = current concentration × available volume ÷ target concentration
- Diluent to add (µL) = normalization final volume − available volume
Standard conversion factors used here are 50 for double-stranded DNA, 33 for single-stranded DNA, and 20 for short oligonucleotides.
How to use this calculator
- Select the correct nucleic acid type for your sample.
- Enter absorbance values at 260 nm, 280 nm, and 230 nm.
- Add the dilution factor used before the spectrophotometer reading.
- Enter the optical path length in millimeters.
- Provide the total solution volume to estimate total recovered DNA.
- Enter available sample volume and a target concentration for normalization planning.
- Click the calculate button to show the result above the form.
- Review concentration, purity ratios, yield, graph, and download options.
Example data table
| Sample | Type | A260 | A280 | A230 | Dilution | Path Length (mm) | Concentration (ng/µL) | A260/A280 | A260/A230 |
|---|---|---|---|---|---|---|---|---|---|
| Leaf Extract 01 | dsDNA | 0.420 | 0.220 | 0.300 | 20 | 10 | 420.00 | 1.909 | 1.400 |
| Buccal Swab 02 | dsDNA | 0.185 | 0.101 | 0.090 | 10 | 10 | 92.50 | 1.832 | 2.056 |
| Primer Pool 03 | Oligo | 0.650 | 0.350 | 0.310 | 5 | 10 | 65.00 | 1.857 | 2.097 |
Frequently asked questions
1. Which conversion factor should I choose?
Use 50 for dsDNA, 33 for ssDNA, and 20 for short oligonucleotides. Choose the option matching your molecule type because the A260-to-mass relationship changes with strand structure and length.
2. Is A260/A280 enough to judge sample quality?
No. A260/A280 helps detect protein contamination, but A260/A230 often reveals salts, phenol, guanidine, or carbohydrates. Reviewing both ratios gives a better quality check before sequencing, cloning, or PCR.
3. Why does path length matter?
Absorbance depends on optical path length. Standard cuvettes usually use 10 mm. Microvolume instruments may use shorter paths, so concentration must be corrected by dividing through the path length in centimeters.
4. Why do I enter the dilution factor?
If you diluted the sample before reading absorbance, multiply concentration by the dilution factor to recover the original stock concentration. A 1:20 dilution means the stock is twenty times more concentrated.
5. Can absorbance replace fluorometric DNA quantification?
Not always. Absorbance is fast and useful for purity ratios, but fluorometric assays are usually better for low-concentration or contaminated samples because they are more selective for nucleic acids.
6. What is a good A260/A280 value for DNA?
Pure DNA often reads near 1.8. Lower values may indicate protein or phenol. Higher values can appear with RNA carryover, baseline problems, or weak absorbance measurements.
7. What is a good A260/A230 value for DNA?
Many clean DNA extracts fall near 2.0 to 2.2. Lower ratios may suggest chaotropic salts, carbohydrates, EDTA, or solvent carryover that can interfere with downstream enzymatic work.
8. How should I normalize samples?
Enter your current concentration, available volume, and desired target concentration. The calculator estimates the final diluted volume and added buffer needed when the current stock is more concentrated than the target.