Absorbance to Transmittance Calculator

Calculator Inputs

Calculation Mode

Choose the chemistry input style that matches your lab data.

Absorbance (A)

Decimal Transmittance (T)

Percent Transmittance (%T)

Sample Intensity (I)

Reference Intensity (I0)

Molar Absorptivity (ε)

Path Length (b, cm)

Concentration (c)

Plotly Graph

This chart shows how absorbance changes transmittance on a logarithmic optical scale.

Example Data Table

Absorbance (A)	Decimal Transmittance (T)	Percent Transmittance (%T)	Fraction Absorbed	Interpretation
0.1000	0.7943	79.43	0.2057	Weak absorption
0.3000	0.5012	50.12	0.4988	Moderate absorption
0.5230	0.3000	30.00	0.7000	Strong absorption
1.0000	0.1000	10.00	0.9000	Very strong absorption
2.0000	0.0100	1.00	0.9900	Near-complete blocking

Formula Used

1) From absorbance to transmittance:
T = 10^-A

2) From decimal transmittance to absorbance:
A = -log₁₀(T)

3) From percent transmittance to absorbance:
A = -log₁₀(%T / 100)

4) From intensity values:
T = I / I₀, then A = -log₁₀(T)

5) Beer–Lambert relation:
A = εbc

Here, A is absorbance, T is decimal transmittance, %T is percent transmittance, I is transmitted intensity, I₀ is incident intensity, ε is molar absorptivity, b is path length, and c is concentration.

How to Use This Calculator

Select the calculation mode that matches your available chemistry data.
Enter absorbance, transmittance, intensity values, or Beer–Lambert inputs.
Press Calculate to display the result above the form.
Review absorbance, decimal transmittance, percent transmittance, and interpretation.
Use the CSV or PDF buttons to export your result.
Study the graph to compare absorbance and transmittance behavior visually.

Frequently Asked Questions

1) What does absorbance measure?

Absorbance measures how much light a sample removes from an incoming beam. Higher absorbance means less light passes through the solution.

2) What is transmittance in chemistry?

Transmittance is the fraction of light that passes through a sample. It may be shown as a decimal ratio or as percent transmittance.

3) Why does high absorbance give low transmittance?

Absorbance and transmittance are logarithmically linked. As a sample absorbs more light, less transmitted light remains, so transmittance drops quickly.

4) Can percent transmittance exceed 100?

No. In standard measurements, percent transmittance should stay between greater than 0 and 100. Values above 100 usually suggest calibration issues.

5) When should I use the intensity method?

Use the intensity method when you directly know sample intensity and reference intensity. The calculator converts their ratio into transmittance and absorbance.

6) What does Beer–Lambert mode do?

Beer–Lambert mode estimates absorbance from molar absorptivity, path length, and concentration. It then converts the absorbance into transmittance values automatically.

7) Is optical density different from absorbance?

In many lab contexts, optical density and absorbance are treated the same. Both describe logarithmic light loss through the sample.

8) What input range is practical for absorbance?

Many instruments perform best within moderate absorbance ranges, often around 0.1 to 1.0. Very high values can reduce measurement reliability.