---
title: "AR Coating Quarter-Wave calculator — AperiOptic"
description: "Single-layer AR ideal physical thickness and ideal index. Free online optics calculator, with the formula and code snippets."
url: "https://aperioptic.com/calculators/ar-coating-quarter-wave"
---

# AR Coating Quarter-Wave calculator

Single-layer AR ideal physical thickness and ideal index.

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

Formula: `d = λ/(4n) · n_ideal = √(n0·ns)`

## Inputs

| Input | Parameter | Unit | Default |
| --- | --- | --- | --- |
| Wavelength | `lam` | nm | 550 |
| Coating n | `n` |  | 1.38 |
| Substrate n | `ns` |  | 1.52 |

## Result with the default inputs

- QW thickness: 99.6377 nm
- Ideal n: 1.2329
- Ideal n (n0=1): 1.2329

Open it with your own values: put each input in the address as a parameter, for example [`/calculators/ar-coating-quarter-wave?lam=550`](https://aperioptic.com/calculators/ar-coating-quarter-wave?lam=550). A unit other than the listed one goes in `<parameter>_unit`.

Read more: [Wikipedia: Anti-reflective coating](https://en.wikipedia.org/wiki/Anti-reflective_coating)

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

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