---
title: "Thin-Film Interference calculator — AperiOptic"
description: "Reflection maximum of a film between lower-index media (one π phase flip, e.g. a soap film). Free online optics calculator, with the formula and code snippets."
url: "https://aperioptic.com/calculators/thin-film-interference"
---

# Thin-Film Interference calculator

Reflection maximum of a film between lower-index media (one π phase flip, e.g. a soap film).

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

Formula: `2·n·t = (m + ½)·λ`

## Inputs

| Input | Parameter | Unit | Default |
| --- | --- | --- | --- |
| λ | `lam` | nm | 550 |
| Film n | `n` |  | 1.38 |
| Order m | `m` |  | 0 |

## Result with the default inputs

- Min thickness: 99.6377 nm
- QWOT: 99.6377 nm

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

Read more: [Wikipedia: Thin-film interference](https://en.wikipedia.org/wiki/Thin-film_interference)

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

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