---
# Don't modify this file manually. This file is auto generated from source, and you will lose your changes next time the website is built.
# Head to the `biomejs/biome` repository, and modify the source code in there.

title: noUnknownUnit
description: Learn more about noUnknownUnit
---
import { Tabs, TabItem } from '@astrojs/starlight/components';

<Tabs>
<TabItem label="CSS" icon="seti:css">
## Summary
- Rule available since: `v1.8.0`
- Diagnostic Category: [`lint/correctness/noUnknownUnit`](/reference/diagnostics#diagnostic-category)
- This rule is **recommended**, meaning it is enabled by default.
- This rule doesn't have a fix.
- The default severity of this rule is [**error**](/reference/diagnostics#error).
- Sources: 
  - Same as [`unit-no-unknown`](https://github.com/stylelint/stylelint/blob/main/lib/rules/unit-no-unknown/README.md)

## How to configure
```json title="biome.json"
{
	"linter": {
		"rules": {
			"correctness": {
				"noUnknownUnit": "error"
			}
		}
	}
}

```
## Description
Disallow unknown CSS units.

For details on known CSS units, see the [MDN web docs](https://developer.mozilla.org/en-US/docs/Learn/CSS/Building_blocks/Values_and_units#lengths).

## Examples

### Invalid

```css
a {
  width: 10pixels;
}
```

<pre class="language-text"><code class="language-text">code-block.css:2:12 <a href="https://biomejs.dev/linter/rules/no-unknown-unit">lint/correctness/noUnknownUnit</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━<br /><br />  <strong><span style="color: Tomato;">✖</span></strong> <span style="color: Tomato;">Unexpected unknown unit: </span><span style="color: Tomato;"><strong>pixels</strong></span><br />  <br />    <strong>1 │ </strong>a &#123;<br />  <strong><span style="color: Tomato;">&gt;</span></strong> <strong>2 │ </strong>  width: 10pixels;<br />   <strong>   │ </strong>           <strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><br />    <strong>3 │ </strong>&#125;<br />    <strong>4 │ </strong><br />  <br />  <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">See </span><span style="color: lightgreen;"><a href="https://developer.mozilla.org/en-US/docs/Learn/CSS/Building_blocks/Values_and_units#lengths">MDN web docs</a></span><span style="color: lightgreen;"> for more details.</span><br />  <br />  <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Use a known unit instead, such as:</span><br />  <br />  - px<br />  - em<br />  - rem<br />  - etc.<br />  <br /></code></pre>

```css
a {
  width: calc(10px + 10pixels);
}
```

<pre class="language-text"><code class="language-text">code-block.css:2:24 <a href="https://biomejs.dev/linter/rules/no-unknown-unit">lint/correctness/noUnknownUnit</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━<br /><br />  <strong><span style="color: Tomato;">✖</span></strong> <span style="color: Tomato;">Unexpected unknown unit: </span><span style="color: Tomato;"><strong>pixels</strong></span><br />  <br />    <strong>1 │ </strong>a &#123;<br />  <strong><span style="color: Tomato;">&gt;</span></strong> <strong>2 │ </strong>  width: calc(10px + 10pixels);<br />   <strong>   │ </strong>                       <strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><br />    <strong>3 │ </strong>&#125;<br />    <strong>4 │ </strong><br />  <br />  <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">See </span><span style="color: lightgreen;"><a href="https://developer.mozilla.org/en-US/docs/Learn/CSS/Building_blocks/Values_and_units#lengths">MDN web docs</a></span><span style="color: lightgreen;"> for more details.</span><br />  <br />  <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Use a known unit instead, such as:</span><br />  <br />  - px<br />  - em<br />  - rem<br />  - etc.<br />  <br /></code></pre>

### Valid

```css
a {
  width: 10px;
}
```

```css
a {
  width: 10Px;
}
```

```css
a {
  width: 10pX;
}
```

```css
a {
  width: calc(10px + 10px);
}
```

## Related links

- [Disable a rule](/linter/#disable-a-rule)
- [Configure the code fix](/linter#configure-the-code-fix)
- [Rule options](/linter/#rule-options)
- [Source Code](https://github.com/biomejs/biome/blob/main/crates/biome_css_analyze/src/lint/correctness/no_unknown_unit.rs)
- [Test Cases](https://github.com/biomejs/biome/blob/main/crates/biome_css_analyze/tests/specs/correctness/noUnknownUnit)

</TabItem>
</Tabs>