BSA standard at A280
Calculate BSA mass and molar concentration from one reading.
Beer–Lambert Law Calculator
FigranSolve A = εlc, or get protein, DNA or RNA concentration and purity ratios from absorbance.
- A = εlc
- Protein A280
- DNA and RNA A260
- Batch samples
Samples
| Sample | A280 | A260 | Dilution | Remove sample |
|---|---|---|---|---|
BSA
A280 · Extinction coefficient
E0.1% 0.667 · 1 cm path · undiluted
0.780 mg/mL11.7 µM
Beer–Lambert law calculator examples
Start with an example and adapt it to your samples.
IgG antibody at 1:10 dilution
Account for dilution when measuring an antibody.
Lysozyme from its sequence
Predict ε from the mature protein sequence and cystines.
Plasmid minipreps with purity ratios
Compare four samples after baseline correction.
Total RNA quality check
Calculate concentration and inspect two purity ratios.
Primer stock from its sequence
Use the DNA sequence to calculate the extinction coefficient.
NADH at 340 nm
Calculate concentration using a known molar coefficient.
Crude lysate with Warburg–Christian
Estimate protein from measurements at two wavelengths.
How to calculate concentration from absorbance
Calculate a concentration in four steps.
1Choose a mode
Select protein, nucleic acid or A = εlc.
2Choose a coefficient
Choose a preset, sequence or known coefficient.
3Enter readings
Enter or paste readings, dilution and path length.
4Save the result
Copy the results or export a CSV.
Beer–Lambert law and extinction coefficients
Absorbance connects concentration, path length and a substance-specific coefficient.
A = ε · l · c
c = A · D / (ε · l)
A = 2 − log₁₀(%T)
| Coefficient | Units | Relationship |
|---|---|---|
| Molar absorption coefficient | M⁻¹ cm⁻¹ | ε |
| Mass coefficient E0.1% | mL mg⁻¹ cm⁻¹ | ε / MW |
| Mass coefficient E1% | Absorbance of a 10 mg/mL solution at 1 cm | 10 × E0.1% |
Coefficients can come from a sequence, a supplier or an experimental measurement. Check the usable range of your instrument.
References: IUPAC Gold Book · Thermo NanoDrop One · Thermo TN52629 (NADH)
Protein concentration from A280
At A280 = 1 and a 1 cm path, the concentration depends on the protein coefficient.
| Protein | ε280 (M⁻¹ cm⁻¹) | MW (g/mol) | E0.1% | mg/mL at A280 = 1 | µM at A280 = 1 |
|---|---|---|---|---|---|
| BSA | 44,309 | 66,430 | 0.667 | 1.50 | 22.6 |
| IgG | 205,500 | 150,000 | 1.37 | 0.730 | 4.87 |
| Lysozyme | 37,970 | 14,313 | 2.65 | 0.377 | 26.3 |
mg/mL = (1.55 · A280 − 0.76 · A260) × D / l
The sequence estimate depends on the cysteine state and can be less reliable without tryptophan.
References: Pace et al. (1995) · Sigma BSA · UniProt P00698 · Thermo NanoDrop purity ratios · GE Spectrophotometry Handbook
DNA and RNA concentration from A260
The conversion factor depends on the nucleic acid and, for short oligos, its sequence.
c = A260 × factor × D / l
| Sample type | Factor (µg/mL per A260) | At A260 = 0.35, dilution ×20 |
|---|---|---|
| dsDNA | 50 | 350.0 ng/µL |
| ssDNA | 33 | 231.0 ng/µL |
| RNA | 40 | 280.0 ng/µL |
| Oligo from sequence | ε260 = 172,500 M⁻¹ cm⁻¹ | 212.2 ng/µL |
A260/A280 and A260/230 purity ratios
| Ratio | Typical value | Possible low value cause | Possible high value cause |
|---|---|---|---|
| DNA A260/A280 | ~1.8 | Phenol or other reagent | pH or measurement variation |
| RNA A260/A280 | ~2.0 | Phenol or other reagent | pH or measurement variation |
| A260/230 | 2.0–2.2 | Salt, guanidine or carbohydrate | Blank or measurement variation |
References: Thermo T042 · Thermo TN52646 · Thermo T123 · Wilfinger et al. (1997) · Glasel (1995) · OligoCalc
Beer–Lambert law calculator FAQ
How do I find concentration from absorbance?
Divide absorbance by ε and path length, then multiply by the dilution factor. For BSA, A280 = 0.52 and E0.1% = 0.667 gives 0.780 mg/mL at 1 cm.
How do I calculate molar absorptivity?
Divide absorbance by concentration and path length. A series of known concentrations can provide a more reliable slope; this calculator solves a single point.
Where do I get my protein’s extinction coefficient?
Use a supplier value or predict it from the amino-acid sequence. The prediction depends on cysteine state and may be less accurate without tryptophan. View more protein properties in the Protein Molecular Weight Calculator.
Can I paste NanoDrop readings?
Yes. Paste a table with recognized column headings. NanoDrop reports 10 mm equivalent absorbance, so use a 1 cm path length. NanoDrop is a Thermo Fisher Scientific trademark.
What A260/A280 and A260/230 ratios mean pure DNA or RNA?
Typical A260/A280 values are about 1.8 for DNA and 2.0 for RNA; A260/230 is commonly 2.0–2.2. Low concentration, pH and contaminants can affect these ratios.
Why use 50 µg/mL for dsDNA, and when should I use a sequence?
The factor is an average for double-stranded DNA. Short oligos vary with base composition, so use a sequence-specific coefficient for an unmodified DNA oligo. To convert DNA concentration to copy number, use the DNA Copy Number Calculator.
How do I convert transmittance to absorbance?
Use A = 2 − log₁₀(%T). A transmittance of 35% corresponds to an absorbance of 0.456.
What absorbance range gives reliable results?
The usable range depends on the instrument and sample. Consult its specifications; for a 1 cm cuvette, high readings may require dilution.
Can I use it for Bradford, BCA or peptide samples?
Bradford and BCA assays require a standard curve. Peptides containing tryptophan or tyrosine can be estimated from their sequence, subject to the method’s limitations. For standard curves use the ELISA Standard Curve Calculator. For solution preparation use the Molarity Calculator.