Enter transmittance values and compute absorbance
Example data table
| Input Mode | Transmittance | Fraction T | Absorbance A10 |
|---|---|---|---|
| Percent | 100 | 1.0000 | 0.0000 |
| Percent | 50 | 0.5000 | 0.3010 |
| Percent | 10 | 0.1000 | 1.0000 |
Formula used in this calculator
1) Convert transmittance to a fraction:
- If you enter %T: T = %T / 100
- If you enter fraction T: use it directly, where 0 < T ≤ 1
2) Optional blank correction:
- Tcorr = Ts / Tb, where Ts is sample, Tb is blank.
3) Absorbance (base-10, standard):
- A10 = −log10(Tcorr)
- Equivalent for percent input without blank: A10 = 2 − log10(%T)
4) Napierian absorbance (optional reporting):
- Ae = −ln(Tcorr), and Ae ≈ 2.303 × A10
How to use this transmittance to absorbance calculator
- Select whether your instrument shows percent or fractional transmittance.
- Enter one reading or multiple replicates separated by commas.
- Optionally enter blank transmittance to correct the sample.
- Choose rounding decimals for consistent reporting in tables.
- Press Calculate to show results above the form.
- Use the export buttons to download CSV or PDF outputs.
Why absorbance is preferred for quantitation
Spectrophotometers often output transmittance because it is a direct intensity ratio. Absorbance is typically used for chemistry reporting because it linearizes many measurements. When T halves, absorbance increases by about 0.301. That makes trends easier to compare across dilutions and batches.
Working ranges and instrument behavior
Practical readings usually target A10 between 0.1 and 1.0. In that band, signal-to-noise is commonly stable and stray light has less impact. Very low transmittance (for example < 1%) can inflate uncertainty because tiny detector changes produce large absorbance swings.
Blank correction and drift control
A blank accounts for solvent, cuvette, and baseline losses. This calculator supports Tcorr = Ts/Tb, which is useful when lamp intensity changes during a run. If blank transmittance is below unity, corrected transmittance tightens replicate agreement and reduces bias. Record blank values with wavelength to maintain traceability.
Replicate statistics for quality checks
The tool summarizes replicates using mean and sample standard deviation. A low SD indicates stable pipetting, consistent cuvette placement, and steady optics. As a rule of thumb, many routine assays aim for SD below 0.005–0.010 absorbance units across three to five readings, depending on method sensitivity.
Link to Beer–Lambert reporting
When molar absorptivity ε and path length l are available, concentration can be estimated from c = A/(ε·l). Use units consistently: if ε is in L·mol⁻¹·cm⁻¹ and l in cm, then c is in mol/L. Exported CSV and PDF outputs help document the values used in calculations.
1) What is the difference between transmittance and absorbance?
Transmittance is the fraction of light that passes through a sample. Absorbance is a logarithmic measure of light loss, computed as A10 = −log10(T), which often supports linear calibration curves.
2) Why must transmittance be greater than zero?
Logarithms are undefined at zero. If the instrument reports extremely small values, treat them as below detection and consider dilution or a shorter path length to keep measurements within a reliable range.
3) When should I use blank correction?
Use blank correction when the solvent, cuvette, or baseline absorbs or scatters light. Correcting with Ts/Tb reduces bias and helps compensate for gradual lamp drift during repeated measurements.
4) What does napierian absorbance mean?
Napierian absorbance uses the natural logarithm: Ae = −ln(T). It is sometimes used in kinetics and physics contexts. It relates to base-10 absorbance by Ae ≈ 2.303 × A10.
5) How many replicates should I enter?
Enter as many as your method requires. Three replicates are common for routine checks, while five or more can help confirm stability for critical assays. The calculator reports mean and sample SD to support acceptance criteria.
6) Can I compute concentration from absorbance here?
Yes, if you provide ε and l, the tool estimates c = A/(ε·l) using the mean absorbance. Ensure units are consistent and match your reference for molar absorptivity.