Protein Concentration A280
Calculator
Results
- Concentration (mg/mL)
- 6.371814
- Concentration (µg/mL)
- 6,371.814092
- Total protein recovered (mg)
- 3.185907
Biology and lab results
| Concentration (mg/mL) | 6.371814 |
| Concentration (µg/mL) | 6,371.814092 |
| Total protein recovered (mg) | 3.185907 |
formula-map diagram
- Concentration (mg/mL)
- 6.371814
- Concentration (µg/mL)
- 6,371.814092
- Total protein recovered (mg)
- 3.185907
Formula breakdown
Formula
C (mg/mL) = A280 × dilution ÷ ε(0.1 %)= 6.3718140929535
Note
Simplified model: these results use standard textbook laboratory relationships and average constants (A260 = 1 for 50 µg/mL dsDNA, 617.96 g/mol per base pair, ~110 Da per amino acid, ideal exponential growth). Real samples vary with purity, contaminants, buffer, temperature and instrument calibration. Always confirm against your own standards and protocol; do not use for diagnostic or safety-critical work.
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See all →Frequently asked questions
Why is 280 nm used to measure protein concentration?+
Aromatic amino acids, mainly tryptophan and tyrosine, along with cystine disulfide bonds, absorb ultraviolet light strongly near 280 nm, so the absorbance at that wavelength scales with how many of these residues are present in the sample.
How does the calculator convert absorbance into concentration?+
It applies the Beer-Lambert law, concentration = A280 / (extinction coefficient x path length), using the protein's molar or percent extinction coefficient that you supply, since this coefficient varies from protein to protein depending on its aromatic residue content.
Why do I need to know the extinction coefficient specifically for my protein?+
Because tryptophan, tyrosine, and cystine content differs between proteins, a generic conversion factor (unlike the DNA A260 case) is not accurate; using a coefficient calculated from your protein's actual sequence, or an experimentally determined one, gives a much more reliable concentration.
Can this method be used for a mixture of different proteins?+
Not reliably for absolute concentration, since a mixture has no single extinction coefficient; A280 for a mixed sample (like crude lysate) is better used as a relative measure of total protein content, or paired with a colorimetric assay such as Bradford or BCA for an absolute value.
What can cause A280 to overestimate protein concentration?+
Contaminants that also absorb near 280 nm, most notably residual nucleic acids, will inflate the reading; a high A260/A280 ratio is a sign of this contamination, and a nucleic-acid correction formula or a cleaner prep should be used if that ratio is elevated.