Turn absorbance readings into transmittance in seconds accurately. See fraction and percent outputs with notes. Built for spectroscopy, filters, and classroom demonstrations every day.
Transmittance is the fraction of light that passes through a sample: T = I / I₀. Absorbance (sometimes called optical density) is a logarithmic measure of attenuation.
Tip: If your absorbance is negative, check blank/reference settings.
| Absorbance (A) | Transmittance (T) | Percent Transmittance (%T) | Typical interpretation |
|---|---|---|---|
| 0.00 | 1.0000 | 100.00% | No attenuation relative to reference. |
| 0.30 | 0.5012 | 50.12% | About half the light is transmitted. |
| 0.60 | 0.2512 | 25.12% | Moderate absorption or scattering. |
| 1.00 | 0.1000 | 10.00% | Strong attenuation; signal may be low. |
Values above assume the base-10 absorbance definition.
Absorbance (A) describes how strongly a sample reduces transmitted light. It is dimensionless and logarithmic, which makes it practical for wide ranges. An increase of 1.00 absorbance unit corresponds to a tenfold decrease in transmittance.
Most instruments use the base-10 definition: A = −log10(T). This calculator returns T = 10−A and %T = 100 × T. For workflows using natural logs, select A = −ln(T) to compute T = e−A.
Common absorbance targets for quantitative work often fall between 0.2 and 1.0. For reference: A = 0.30 gives T ≈ 0.501 (≈50.1%), A = 0.60 gives T ≈ 0.251 (≈25.1%), and A = 1.00 gives T = 0.100 (10%).
Very high absorbance can push measurements into noise. At A = 2.0, transmittance is about 1%, and small stray light can dominate results. At A = 3.0, transmittance drops to 0.1%, which is often beyond reliable photometric range.
Negative absorbance implies T > 1, meaning the sample appears brighter than reference. This usually indicates a blank mismatch, baseline drift, or incorrect I0. Re-zero the instrument, confirm cuvette orientation, and verify the reference solution.
Many reports include both A and %T for clarity. Use consistent wavelength, path length, and instrument settings. Keep significant figures aligned with measurement uncertainty, and record any smoothing, averaging, or baseline correction applied.
In Beer–Lambert applications, absorbance scales with concentration and path length. Converting to transmittance helps visualize signal levels and detector saturation. If %T is extremely low, consider dilution or shorter path length for better precision.
Base-10 absorbance is standard for spectrophotometers and analytical chemistry. Natural-log absorbance appears in physics derivations and radiative attenuation models. Choose the definition that matches your instrument documentation and calculation pipeline.
T is the fraction I/I0 from 0 to 1. %T is simply 100 × T, which is often easier to read in reports.
Because absorbance is logarithmic. An increase of 0.30 reduces transmittance by about half, so small A shifts can noticeably change signal levels.
A = 1.2 corresponds to about 6.3% transmittance. It may be usable, but noise and stray light can increase. If precision is important, consider dilution.
This usually comes from negative absorbance caused by blank mismatch, baseline drift, or reference errors. Re-blank the instrument and verify I0 conditions.
Use base-10 if your spectrophotometer reports absorbance (most do). Use the natural definition if your method explicitly uses ln-based attenuation.
The math does not, but your measured absorbance depends strongly on wavelength. Always record wavelength and bandwidth when documenting results.
Yes. If you have absorbance-like attenuation values, converting to transmittance helps compare filter stacks, coating performance, and system throughput.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.