Protein Concentration Calculator

What This Calculator Does

This calculator converts a UV absorbance reading at 280 nm (A280) into protein concentration, using the Beer-Lambert law and your protein’s specific extinction coefficient and molecular weight.

The Formula

The Beer-Lambert law states A = ε × c × l, where A is absorbance, ε is the molar extinction coefficient, c is molar concentration, and l is the path length in cm. Solving for concentration gives c = A / (ε × l). This molar concentration is then multiplied by the protein’s molecular weight (and any dilution factor) to give a mass concentration in mg/mL.

• Extinction coefficients are protein-specific and are often calculated from a protein’s amino acid sequence (e.g., via ProtParam) or found in the literature.
• If you diluted your sample before reading absorbance, enter that dilution factor to get the concentration of the original sample.

This tool is for general lab reference and educational purposes. Using an inaccurate extinction coefficient or molecular weight will proportionally affect the result, so double-check these values for your specific protein.