π Absorbance β Transmittance Converter
Convert between absorbance (A) and percent transmittance (%T) using the standard logarithmic relationship.
Frequently asked questions
What's the difference between absorbance and transmittance?
Transmittance (T) is the fraction of incident light that passes through a sample (T=1 means all light passes; T=0 means none does). Absorbance (A) is the logarithmic form, A = -log10(T), used because it's directly proportional to concentration via the Beer-Lambert Law, unlike transmittance.
Why is absorbance used instead of transmittance for concentration calculations?
Absorbance scales linearly with concentration and path length (A = epsilon * c * l), which makes calibration curves straightforward. Transmittance has an exponential relationship with concentration, so it isn't used directly for quantification.
What does 0% transmittance mean?
0% T means no light passes through the sample at all, which corresponds to an absorbance of infinity mathematically. In practice this usually indicates the sample is too concentrated or opaque for accurate measurement at that wavelength β dilute and re-measure.
Accuracy & how this is derived
Derivation: Direct logarithmic relationship A = -log10(T), the standard definition of absorbance in spectroscopy, algebraically inverted for the reverse conversion.
Validated against: Standard spectroscopy definition used in all UV-Vis instrumentation and analytical chemistry textbooks.
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β Last updated: July 2026 Β· Report an error
Converting between absorbance and transmittance
Absorbance and transmittance describe the same physical measurement β how much light passes through a sample β but on different scales. Transmittance is a direct linear fraction of light transmitted, while absorbance is its negative base-10 logarithm, chosen because it scales linearly with analyte concentration and path length under the Beer-Lambert Law, which is why absorbance rather than transmittance is used for quantitative spectroscopic analysis.