Spectrophotometry Calculators: Absorbance and Concentration

Use these spectrophotometry calculators to work with the light absorbed or transmitted by a solution. The Beer–Lambert Law calculator helps you find absorbance, concentration, or transmittance from measurements such as incident and transmitted light intensity, molar absorptivity, and path length. It is useful for students checking lab calculations, researchers analyzing samples, and anyone preparing or comparing chemical solutions. Enter the values you know to solve for the missing quantity and see how light measurements relate to concentration.

Photon Energy

Calculate the energy of a photon from its wavelength or frequency. Enter either value and get the energy per photon in joules and electronvolts, plus the energy per mole of photons in kJ/mol.

Chromatography Retention Factor

Calculate the chromatographic retention factor k′ from the analyte retention time and the column dead time. Enter both times in any unit and get k′, the adjusted retention time, and an interpretation.

Chromatography Theoretical Plates

Calculate the number of theoretical plates (N) of a chromatographic column from a peak's retention time and width, using either the half-height (USP/Ph. Eur.) or baseline method. Optionally enter the column length to get the plate height (HETP).

Beer–Lambert Law

Enter molar absorptivity, concentration, and path length to calculate a solution’s absorbance and percent transmittance using the Beer–Lambert law.

Rydberg Equation

Enter the initial and final principal quantum numbers of a hydrogen electron transition and get the wavelength, frequency and photon energy of the spectral line, plus its series (Lyman, Balmer, Paschen…).

Chromatography Selectivity Factor

Enter the retention times of two compounds and the column dead time to compute the selectivity factor (α) and both retention factors, and see how well the column separates the pair.