DNA/RNA Concentration Calculator
Enter the A260 absorbance, nucleic-acid type (dsDNA/ssDNA/RNA), dilution factor, and path length to instantly compute nucleic-acid concentration (μg/mL and ng/μL), with a reference table of common conversion factors.
Input Data
Results
At a glance:Nucleic-acid concentration can be quantified quickly from UV absorbance: DNA and RNA bases absorb maximally at 260 nm, and absorbance is proportional to concentration (Beer–Lambert law). Apply the standard conversion factor CF: C = (A260 / l) × CF × DF, where dsDNA is about 50 μg/mL per A260, ssDNA about 33, RNA about 40, l is path length, and DF is the dilution factor.
Formula
Concentration: C (μg/mL) = (A260 ÷ l) × CF × DF.
Conversion factor CF: dsDNA=50, ssDNA=33, ssRNA=40 (μg/mL per A260).
μg/mL and ng/μL are numerically equal (1 μg/mL = 1 ng/μL).
$$C = \dfrac{A_{260}}{l} \times \mathrm{CF} \times \mathrm{DF}$$How to Use
- Enter the absorbance A260 measured at 260 nm.
- Choose the nucleic-acid type (dsDNA/ssDNA/RNA) to apply its conversion factor, and enter dilution factor and path length.
- The result shows concentration (μg/mL and ng/μL) on the right.
Nucleic-acid types and A260 conversion factors
| Nucleic-acid type | Conversion factor CF | Concentration per 1.0 A260 |
|---|---|---|
| Double-stranded DNA (dsDNA) | 50 | 50 μg/mL |
| Single-stranded DNA (ssDNA) | 33 | 33 μg/mL |
| RNA (ssRNA) | 40 | 40 μg/mL |
| Oligonucleotide | sequence-dependent | use extinction coefficient ε₂₆₀ |
Purity can be checked via A260/A280: pure DNA ≈ 1.8, pure RNA ≈ 2.0; lower means protein or phenol contamination.
Case Studies
Plasmid DNA quantification
After extraction, take 10 μL plasmid + 190 μL TE buffer (20× dilution), measured A260 = 0.45.
C = (0.45 ÷ 1) × 50 × 20 = 450 μg/mL, i.e. 450 ng/μL.
Use this concentration to compute the volume needed for downstream reactions (ligation, transfection) and avoid under- or over-dosing.
RNA sample quantification
After total RNA extraction, measure undiluted (DF=1), A260 = 0.2, path length 1 cm.
C = (0.2 ÷ 1) × 40 × 1 = 8 μg/mL.
RNA uses CF=40; using DNA's 50 would overestimate by 25%, so choosing the right type matters.
FAQ
Why does dsDNA use 50 but RNA uses 40?
Because different nucleic acids have different molar absorptivity at 260 nm due to base composition and structure. Empirically: 1.0 A260 ≈ 50 μg/mL dsDNA, 33 μg/mL ssDNA, 40 μg/mL RNA. Using the wrong factor systematically over- or under-estimates concentration.
How do I fill the dilution factor?
Enter the factor by which you diluted the sample before measurement. E.g. 5 μL sample + 95 μL water dilutes 20×, so enter 20; for the neat sample enter 1. The tool multiplies the diluted concentration by this factor to recover the stock concentration.
Why are μg/mL and ng/μL the same?
Because 1 μg/mL = 1000 ng ÷ 1000 μL = 1 ng/μL — the two are numerically identical, just different conventional units; molecular-biology work usually uses ng/μL.
What does the A260/A280 ratio mean?
It indicates purity: pure DNA ≈ 1.8, pure RNA ≈ 2.0. A noticeably low ratio means protein (280 nm absorption) or phenol contamination, so purify before quantifying. This calculator only converts concentration; purity requires a separate A280 reading.
Can I use this formula for oligonucleotides (primers)?
Short oligos' absorbance varies strongly with sequence; the accurate approach is to compute the extinction coefficient ε₂₆₀ for that sequence by the nearest-neighbor model and convert. The fixed factors here suit general dsDNA, ssDNA, and RNA samples.
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References
Content review: Calculatorism Science Team. Results are for reference only; please refer to the relevant authorities for the official figures.