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Optical Density

Convert optical density (OD), transmission, dB attenuation and ND filter factor with presets.

Model: Exact

2
0–8

Optical density

2.000

OD = −log₁₀ T

Transmission

1.000 %

blocked 99.00 %

Attenuation

20.0 dB

10 · OD

Filter factor 1/T

100.0

6.64 photographic stops (log₂ 1/T)

Reference Values

OD 0.1 → 79.43% T

OD 0.3 → 50.12% T

OD 1 → 10.00% T

OD 2 → 1.000% T

OD 3 → 0.1000% T

OD 4 → 0.01000% T

OD 6 → 0.0001000% T

OD = −log₁₀(T)

T = 10^(−OD)

Attenuation (dB) = 10 log₁₀(1/T) = 10 × OD

A neutral-density filter labelled "ND 2.0" or "OD 2" transmits 1 %. Photographic ND numbers are filter factors instead (ND8 = 1/T = 8, three stops, OD 0.9). For a sample, OD counts everything that leaves the beam, scattering included; absorbance counts only absorption, and the two agree for a clear solution. The transmission entered here can't exceed 100 %.

Reference: IUPAC Compendium of Chemical Terminology (Gold Book), "absorbance" and "transmittance".

Transmission and loss vs optical density

1.0e-61.0e-51.0e-41.0e-30.010.10110100012345678Optical Density (OD)Percentage (%)
  • Transmission (%)
  • Absorbed or scattered (%)
  • Current

Model and references

Exact. The equations are exact within the stated assumptions, or are a standard's tabulated values. The results are as good as the inputs. About the tiers

Exact definitions: OD = −log₁₀ T, attenuation 10·OD dB, filter factor 1/T and log₂(1/T) stops. For a sample, OD includes scattering losses as well as absorption.

  1. IUPAC Compendium of Chemical Terminology (Gold Book), entries “absorbance” and “transmittance”.
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