---
title: "Transmission ↔ OD ↔ dB calculator — AperiOptic"
description: "Convert between transmission %, optical density and dB attenuation. Free online optics calculator, with the formula and code snippets."
url: "https://aperioptic.com/calculators/transmission-od-db"
---

# Transmission ↔ OD ↔ dB calculator

Convert between transmission %, optical density and dB attenuation.

Category: [Unit Converters](https://aperioptic.com/calculators)

Formula: `OD = -log₁₀(T) · dB = 10·OD`

## Inputs

| Input | Parameter | Unit | Default |
| --- | --- | --- | --- |
| Transmission | `T` | % | 50 |

## Result with the default inputs

- Transmission: 50 %
- Optical density: 0.301 OD
- Attenuation: 3.0103 dB
- Absorbance: 0.301

Open it with your own values: put each input in the address as a parameter, for example [`/calculators/transmission-od-db?T=50`](https://aperioptic.com/calculators/transmission-od-db?T=50). A unit other than the listed one goes in `<parameter>_unit`.

Read more: [Wikipedia: Absorbance](https://en.wikipedia.org/wiki/Absorbance)

[All optics calculators](https://aperioptic.com/calculators)

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The interactive page: https://aperioptic.com/calculators/transmission-od-db (AperiOptic runs in the browser; free, no account). Every page of the site as Markdown: https://aperioptic.com/llms.txt