Calculator Inputs
Enter transmittance data below. The calculated result will appear above this form after submission.
Plotly Graph
This graph shows the inverse relationship between percent transmittance and absorbance. Example points are included, and your latest result is highlighted.
Example Data Table
These example chemistry readings show how absorbance rises as transmittance falls.
| Example | %T | Decimal T | Absorbance | Wavelength (nm) |
|---|---|---|---|---|
| Standard 1 | 95.00 | 0.950000 | 0.022276 | 540 |
| Standard 2 | 80.00 | 0.800000 | 0.096910 | 540 |
| Standard 3 | 60.00 | 0.600000 | 0.221849 | 540 |
| Standard 4 | 35.00 | 0.350000 | 0.455932 | 540 |
| Standard 5 | 12.00 | 0.120000 | 0.920819 | 540 |
Formula Used
Primary transmittance formula: T = I / I0
Absorbance from decimal transmittance: A = -log10(T)
Absorbance from percent transmittance: A = 2 - log10(%T)
Blank-corrected transmittance: Tcorrected = Tsample / Tblank
Beer-Lambert relationship: A = εlc
Transmittance compares transmitted light with incident light. Absorbance increases when less light passes through the sample. The calculator first converts all transmittance values into decimal form. It then applies the logarithmic absorbance equation. When a blank is supplied, the calculator corrects the sample reading before computing absorbance.
If you also provide path length and molar absorptivity, the page estimates concentration from the measured absorbance. If concentration is already known, it also compares measured absorbance with the theoretical Beer-Lambert value.
How to Use This Calculator
- Enter a sample name to identify the reading.
- Type the measured sample transmittance.
- Select whether the value is decimal T or %T.
- Enter the blank or reference transmittance.
- Select the blank input type.
- Add wavelength if you want better recordkeeping.
- Enter path length for Beer-Lambert support.
- Add molar absorptivity and concentration if available.
- Choose the displayed decimal precision.
- Press Calculate Absorbance to show the result above the form.
- Use the CSV or PDF buttons to export the report.
Frequently Asked Questions
1) What does T mean in this calculator?
T means transmittance. It measures how much light passes through a sample relative to the incident light. Higher transmittance usually means lower absorbance.
2) How is absorbance calculated from decimal transmittance?
Absorbance equals negative base ten logarithm of decimal transmittance. The equation is A = -log10(T). A smaller T produces a larger absorbance value.
3) How do I convert percent transmittance to absorbance?
First convert percent transmittance into decimal form by dividing by 100. Then apply A = -log10(T). The calculator performs both steps automatically.
4) Why can absorbance become negative?
Negative absorbance usually means the corrected sample transmittance is greater than the blank or reference. This can happen because of baseline drift, noise, or data entry mistakes.
5) Why does the calculator ask for a blank value?
The blank value helps remove background absorption from solvent, cuvette, or instrument effects. That correction improves the reported absorbance for the actual sample.
6) What is the role of wavelength?
Wavelength identifies the measurement condition used during spectroscopy. It does not change the arithmetic conversion directly, but it helps document and compare lab readings correctly.
7) When are path length and molar absorptivity useful?
They are useful when you want concentration estimates from Beer-Lambert law. If ε and path length are known, the calculator can estimate concentration from measured absorbance.
8) What do the CSV and PDF exports include?
The exports include the current result table and the example dataset. That makes it easier to save readings, share reports, or document laboratory calculations.