Absorbance Concentration Calculator

Calculator Inputs

Enter any known values, choose what to solve, and submit. The page calculates the missing Beer-Lambert variable and plots absorbance versus concentration.

Sample Name

Solve For

Wavelength (nm) - Optional

Absorbance (A)

Concentration (mol/L)

Molar Absorptivity (L·mol⁻¹·cm⁻¹)

Path Length (cm)

Formula Used

Beer-Lambert Law: A = ε × l × c

Concentration: c = A / (ε × l)

Absorbance: A = ε × l × c

Molar Absorptivity: ε = A / (l × c)

Path Length: l = A / (ε × c)

Transmittance: T = 10^-A

Percent Transmittance: %T = T × 100

Absorbance is dimensionless. Concentration is usually entered in mol/L, path length in cm, and molar absorptivity in L·mol⁻¹·cm⁻¹. The plotted line uses the slope εl, which represents the calibration sensitivity.

How to Use This Calculator

Select the variable you want to solve.
Enter the known Beer-Lambert values in the input boxes.
Optionally add a sample name and wavelength for context.
Press Calculate to show the result above the form.
Review the summary table, transmittance values, and calibration equation.
Use the graph to visualize how absorbance changes with concentration.
Download the result as CSV or PDF for lab records.

Example Data Table

Sample	Absorbance (A)	Molar Absorptivity	Path Length (cm)	Concentration (mol/L)	Wavelength (nm)
Blue Dye A	0.300	15000	1.00	2.00e-5	610
Blue Dye B	0.450	15000	1.00	3.00e-5	610
Food Color C	0.620	15500	1.00	4.00e-5	540
Reference Solution	0.180	12000	1.00	1.50e-5	520

Frequently Asked Questions

1) What does this calculator measure?

It applies the Beer-Lambert law to relate absorbance, concentration, path length, and molar absorptivity. It also estimates transmittance and plots the absorbance-concentration trend for quick interpretation.

2) What units should I use?

Use absorbance as a unitless value, concentration in mol/L, path length in centimeters, and molar absorptivity in L·mol⁻¹·cm⁻¹. Keeping units consistent is essential for correct results.

3) Why is my concentration extremely small?

Small concentrations are common when molar absorptivity is large or absorbance is modest. The page automatically formats tiny values in scientific notation so they remain readable and accurate.

4) Can I solve for absorbance instead of concentration?

Yes. Change the solve mode at the top of the form. The calculator can solve for concentration, absorbance, molar absorptivity, or path length using the same Beer-Lambert relationship.

5) What does the plotted line represent?

The graph shows the theoretical linear relationship between concentration and absorbance for the current slope εl. Your calculated sample point is added to the chart for context.

6) What if absorbance is negative?

Negative absorbance usually indicates measurement or baseline issues rather than a valid sample result. This calculator blocks negative absorbance because standard Beer-Lambert analysis expects nonnegative values.

7) How are transmittance values calculated?

Transmittance is derived from absorbance using T = 10^-A. Percent transmittance is simply that fraction multiplied by 100, which gives a more familiar laboratory reporting format.

8) When should I use wavelength input?

Wavelength is optional and does not change the math directly. It is useful for documentation because molar absorptivity depends on wavelength, and many laboratories track readings by wavelength.