---
title: "Coherence Length & Time calculator — AperiOptic"
description: "Longitudinal coherence from spectral bandwidth (Gaussian). Free online optics calculator, with the formula and code snippets."
url: "https://aperioptic.com/calculators/coherence-length-time"
---

# Coherence Length & Time calculator

Longitudinal coherence from spectral bandwidth (Gaussian).

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

Formula: `Lc = (2 ln2 / π) · λ²/Δλ · τc = Lc/c`

## Inputs

| Input | Parameter | Unit | Default |
| --- | --- | --- | --- |
| Center λ | `lam` | nm | 800 |
| Δλ FWHM | `dlam` | nm | 30 |

## Result with the default inputs

- Coherence length: 9.4138 µm
- Coherence time: 31.401 fs

Open it with your own values: put each input in the address as a parameter, for example [`/calculators/coherence-length-time?lam=800`](https://aperioptic.com/calculators/coherence-length-time?lam=800). A unit other than the listed one goes in `<parameter>_unit`.

Read more: [Wikipedia: Coherence length](https://en.wikipedia.org/wiki/Coherence_length)

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

---

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