Solve A = εbc for absorbance, molar absorptivity, optical path length, or molar concentration, with cm/mm/m and mol/L/mmol/L/umol/L conversions.
Introductory analytical chemistry
Your result
Enter your values and press Calculate to see your answer and all five solution steps.
A = εbc
Common Mistakes
Using b in mm or m directly with ε in L/(mol·cm). Convert b to cm first.
Using mmol/L or µmol/L as if it were mol/L. Convert concentration to mol/L before applying the equation.
Treating absorbance as a percent. A is dimensionless and is not a percentage.
Applying a single-species equation to a mixture whose absorbing components or equilibria change with concentration.
Assumptions and limitations
Supported chemical scope: one homogeneous, non-scattering, dilute solution containing one independently absorbing species at one fixed wavelength. ε must correspond to that analyte, solvent, wavelength, and temperature/conditions.
Beer–Lambert behavior is an approximation: use essentially monochromatic light and a blank/calibration curve. High concentration, chemical equilibria, polychromatic or stray light, scattering, and detector saturation can cause deviations.
A = 0 is valid when no division by zero is required. ε = 0 can mean no absorption at the selected wavelength; equations with a zero denominator may be indeterminate rather than numerically solvable.
A = εbc
Learn More
Connect the calculation to your chemistry course and try a related tool.
I teach Chemistry online for IGCSE, GCSE, A Level, AP Chemistry and university students. We can work through the reasoning behind your calculation, step by step, in a lesson on Preply.
Book a Trial LessonThe calculators stay free. Booking is optional and takes place on Preply.
