# calc()

Does math in CSS, even mixing units.

## What does `calc()` do?

`calc()` does math in CSS, even mixing units, like "the full width minus the sidebar".

```css
.main { width: calc(100% - 250px); }   /* room left beside a 250px sidebar */
```

Level: Freelancer · [More CSS terms at this level](https://www.ask-codey.com/glossary/subjects/css/freelancer)

Updated: September 27, 2026

Source: https://www.ask-codey.com/glossary/calc