How to use the Beer-Lambert Law Calculator
Start by choosing the quantity you want to find in Solve for. Enter the other three values, select compatible units, and click Calculate. The result shows the selected quantity, normalized values, and the calculation steps.
- Choose the unknown in Solve for.
- Enter the other three values and select Concentration unit, Path length unit, and Absorptivity unit.
- Click Calculate to show the result and Formula & steps.
- Click Copy result or Download result (.txt). Click Reset to clear the inputs and result.
How the formula and units are handled
The calculator uses A = ε × c × l. Absorbance has no unit. For molar absorptivity, the script converts concentration to mol/L. For mass absorptivity, it keeps concentration in g/L. Path length is converted to centimeters before calculation.
Use mol/L (M), mmol/L (mM), or µmol/L (µM) with molar absorptivity. Use g/L with mass absorptivity. The selected Path length unit can be centimeters (cm), millimeters (mm), or meters (m).
Absorbance (A): 0.85
Concentration (c): 0.002 mol/L (M)
Path length (l): 1 cm
Result: Absorptivity (ε) = 425 L·mol−1·cm−1This example uses Absorptivity (ε) in Solve for. Formula & steps shows concentration in mol/L and path length in cm, the normalized values used for the calculation. The result keeps the selected absorptivity unit.
What values does the Beer-Lambert Law Calculator accept?
Concentration, path length, and absorptivity must be greater than zero. Absorbance can be zero. Empty fields, disallowed negative values, non-finite values, and values with a magnitude above 1,000,000,000,000 are rejected. Enter decimal syntax such as 0.002. Scientific notation such as 1e-3, comma separators, plus signs, and other text are rejected.
Concentration and absorptivity must use a matching pair. Molar absorptivity accepts mol/L (M), mmol/L (mM), or µmol/L (µM); mass absorptivity requires g/L. Changing an input or selection hides the current result until you click Calculate again.
Which quantity should you solve for?
Choose Absorptivity (ε) when absorbance, concentration, and path length are known. The calculator applies the formula and displays the result in the selected molar or mass unit.
Choose Concentration (c) when absorbance, path length, and absorptivity are known. Pick a concentration unit that matches the absorptivity unit before you calculate.
Choose Path length (l) when the other three values are known. The result uses the selected centimeters (cm), millimeters (mm), or meters (m) unit.
Beer-Lambert calculator or another science calculator?
Use Science Calculators to choose among physics, chemistry, electrical, optics, wave, fluid, gas, and radioactive-decay calculations. Choose the Molarity Calculator when the unknown comes from solute amount and solution volume. Choose the Chemistry Calculator when you need pH, dilution, molar mass, stoichiometry, or other chemistry calculations.
Frequently Asked Questions
How do I use the Beer-Lambert law calculator to solve for concentration?
Choose Concentration (c) in Solve for, enter absorbance, path length, and absorptivity, then click Calculate. Select a matching concentration and absorptivity unit before calculating.
What is the Beer-Lambert law formula used by the calculator?
The formula is A = ε × c × l, with A for absorbance, ε for absorptivity, c for concentration, and l for path length. The calculator rearranges it for the quantity selected in Solve for.
What units can I use for a Beer-Lambert calculation?
You can use mol/L (M), mmol/L (mM), or µmol/L (µM) with molar absorptivity, and g/L with mass absorptivity. Path length accepts cm, mm, or m.
Why was my Beer-Lambert calculation rejected?
The calculator rejects missing values, disallowed negative or zero values, invalid number syntax, values above 1,000,000,000,000, and mismatched concentration and absorptivity units. Enter the three known values in decimal form and select a matching unit pair.
Does the calculator account for experimental deviations from the Beer-Lambert law?
No. It applies the supplied numbers to the ideal linear formula. It does not inspect wavelength or species, look up absorptivity, or model high-concentration effects, equilibria, scattering, stray light, or instrument non-linearity.