---
title: "Snell's Law calculator — AperiOptic"
description: "Refraction angle across an interface. Free online optics calculator, with the formula and code snippets."
url: "https://aperioptic.com/calculators/snells-law"
---

# Snell's Law calculator

Refraction angle across an interface.

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

Formula: `n₁ sin θ₁ = n₂ sin θ₂`

## Inputs

| Input | Parameter | Unit | Default |
| --- | --- | --- | --- |
| n₁ | `n1` |  | 1 |
| n₂ | `n2` |  | 1.5 |
| θ₁ | `th1` | ° | 30 |

## Result with the default inputs

- θ₂: 19.4712 °

Open it with your own values: put each input in the address as a parameter, for example [`/calculators/snells-law?n1=1`](https://aperioptic.com/calculators/snells-law?n1=1). A unit other than the listed one goes in `<parameter>_unit`.

Read more: [Wikipedia: Snell's law](https://en.wikipedia.org/wiki/Snell%27s_law)

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

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