OD–Transmission Converter

Convert between optical density (OD) and percent transmission. Calculate total OD and transmission for stacked filters.

Optical density (OD) is the base-10 logarithm of the attenuation factor: OD = −log₁₀(T), where T is fractional transmission. An OD 2 filter passes 1% of incident light; OD 6 passes one part in 10⁶. Because OD values add when filters are stacked in series, laser safety and spectroscopy applications routinely express attenuation logarithmically. This converter translates between OD and percent transmission in both directions and separately computes the combined OD and total transmission for a stack of identical filters. Inputs accept OD values from 0 to 10 and percent transmission from 0.000001% upward. The stacked-filter section assumes negligible inter-filter reflection losses, which is valid for most neutral-density filter applications.

Input
Stacked Filters
OD → Transmission
Optical density (OD)
Input value
2.0000
Fractional transmission (T)
T = 10^(−OD)
0.01000
Percent transmission (%T)
%T = T × 100
1.0000%
Attenuation factor
1/T
100.00×
Stacked Filters
Configuration
2× OD 2.0000
Total OD
OD_total = n × OD_individual
4.0000
Total %T
0.0100%
Total attenuation
10000.0×
Abridged Optics — OD–Transmission Converter v1.0Optical density: OD = −log₁₀(T). Transmission: T = 10^(−OD). Stacked filters: OD_total = n × OD_individual (assumes negligible inter-filter reflections).

All information, equations, and calculations have been compiled and verified to the best of our ability. For mission-critical applications, we recommend independent verification of all values. If you find an error, please let us know.