• Unknown pure proteins or protein mixtures: Use the following formula to roughly estimate protein concentration.
Protein Concentration (mg/ml) = OD280 divided by cuvette width (cm)

• Pure protein of known absorbance coefficient.
Protein concentration = OD280 divided by (absorbance coefficient * cuvette width)

• Unknown protein with possible nucleic acid contamination. Use the following formula to estimate protein concentration:
Protein Concentration (mg/ml) = (1.55 * OD280) - (0.76 * OD260)