Determine protein concentration from absorbance using the Beer-Lambert law.
The Beer-Lambert law is linear only between roughly 0.05 and 1.5 absorbance units. Outside that window, stray light and detector saturation make readings unreliable regardless of the arithmetic. Absorbance at 280 nm depends on tryptophan and tyrosine content, so the extinction coefficient is protein-specific and must not be assumed.
Protein Concentration
A = ε c l, so c = A ÷ (ε l), then × dilution factor
A = ε c l, so c = A ÷ (ε l), then × dilution factor The Beer-Lambert law is linear only between roughly 0.05 and 1.5 absorbance units. Outside that window, stray light and detector saturation make readings unreliable regardless of the arithmetic.
Absorbance at 280 nm depends on tryptophan and tyrosine content, so the extinction coefficient is protein-specific and must not be assumed.
This calculator takes 5 inputs: Absorbance at 280 nm, Molar extinction coefficient, Path length, Protein molecular weight, Dilution factor. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.