Protein Concentration Calculator

What Is Protein Concentration and How Is It Measured?

Protein concentration is a measure of how much protein is present in a given volume of solution. It is a fundamental parameter in biochemistry, molecular biology, and biopharmaceutical development. Researchers use it to standardize samples, prepare assays, and quantify protein yields after purification. The most common method for estimating protein concentration is UV absorbance spectrophotometry at 280 nm, where aromatic amino acids (tryptophan, tyrosine, and phenylalanine) absorb light strongly.

The Beer-Lambert Law for Protein Concentration

Protein concentration is calculated using the Beer-Lambert Law, which relates absorbance to concentration:

$$A = \varepsilon \times b \times C$$

Rearranging for concentration and accounting for molecular weight and dilution:

$$C = \frac{A}{\varepsilon \times b} \times m \times n$$

where:

• $C$ is the protein concentration (in mg/mL)
• $A$ is the absorbance measured at 280 nm
• $\varepsilon$ is the extinction coefficient (M⁻¹ cm⁻¹)
• $b$ is the pathlength of the cuvette (cm)
• $m$ is the molecular mass of the protein (g/mol)
• $n$ is the dilution factor

For example, a BSA sample with an absorbance of 0.5 at 280 nm, measured in a 1 cm cuvette with no dilution, gives a concentration of:

$$C = \frac{0.5}{43824 \times 1} \times 66463 \times 1 \approx 0.758 \text{ mg/mL}$$

Using the Protein Concentration Calculator

Select your protein from the preset list, which includes common proteins like BSA, IgG, Lysozyme, and more, each with pre-loaded extinction coefficients and molecular weights. If your protein is not listed, choose "Custom Protein" and enter the values manually. Enter your absorbance reading at 280 nm, the cuvette pathlength (typically 1 cm), and the dilution factor (use 1 for undiluted stock). Choose your preferred output unit from mg/mL, ug/mL, g/L, M, or mM. The calculator instantly displays the concentration along with a full breakdown of the calculation.

Important Considerations

UV absorbance at 280 nm is a quick and non-destructive method, but it can be affected by the presence of nucleic acids, which also absorb at 280 nm. For more accurate results in complex samples, consider using the Bradford assay or BCA assay. Always measure your sample against a blank (buffer-only) reference to eliminate background absorbance. Our calculator gives results based on the standard Beer-Lambert relationship and assumes a pure protein sample.

For related biochemistry tools, try the Beer Lambert Law Calculator and the Protein Molecular Weight Calculator.