Use the Beer-Lambert Law Calculator
Use any three of these values to solve for the fourth: absorbance, concentration, path length, or absorptivity. The calculator applies A = ε × c × l and shows the normalized values and calculation steps.
Choose the Quantity and Units
Choose the unknown from Solve for. Then select the units from Concentration unit, Path length unit, and Absorptivity unit. Match molar absorptivity with M, mM, or µM; match mass absorptivity with g/L. Internally, the calculator uses mol/L or g/L for concentration and centimeters for path length.
Calculate a Result
- Enter the other three values as plain decimal numbers.
- Choose Solve for and select the relevant unit options.
- Click Calculate. The result shows the formula, normalized values, and calculation steps.
- Click Copy result to copy the plain-text result, or click Download result (.txt) to save
beer-lambert-law-calculator-result.txt. - Click Reset to clear the inputs and result.
Enter Accepted Numbers
Enter finite numeric values. Absorbance may be zero; concentration, path length, and absorptivity entered as known values must be greater than zero. The calculator rejects empty, negative, non-matching, and oversized values. Use plain decimal syntax such as 0.002; scientific notation such as 1e-3, comma-formatted values, plus signs, and other text are rejected. A calculated concentration, path length, or absorptivity may be zero when absorbance is zero.
Calculation Scope and Limitations
The calculator applies the ideal linear relationship to the numbers and units you supply. It does not inspect species, wavelength, or experimental conditions, look up absorptivity values, or model deviations caused by high concentration, chemical equilibria, scattering, stray light, or instrument non-linearity.
Calculator values are processed locally by the calculator script. The page also has separate analytics, server-side tool-view counting, and subscription requests, so this local calculation statement does not describe every network activity on the page.
Frequently Asked Questions
What is the Beer-Lambert law formula?
The Beer-Lambert law is A = ε × c × l, where A is absorbance, ε is absorptivity, c is concentration, and l is path length.
Can this calculator solve for concentration, path length, or absorptivity, not just absorbance?
Yes. Choose the quantity from Solve for, then enter the other three known values. The calculator rearranges the formula to isolate the selected quantity.
What units does this calculator support?
Concentration supports mol/L (M), mmol/L (mM), µmol/L (µM), and g/L. Path length supports cm, mm, and m. Molar absorptivity requires a molar concentration unit; mass absorptivity requires g/L. Absorbance is unitless.
Why does my absorptivity unit have to match my concentration unit?
Molar absorptivity requires M, mM, or µM, while mass absorptivity requires g/L. The calculator rejects a mismatch instead of guessing a conversion.
Does this tool account for deviations from the Beer-Lambert law?
No. It calculates the ideal linear relationship only. It does not model or correct for deviations from high concentration, chemical equilibria, scattering, stray light, or instrument non-linearity.