# Border box

Width and height include padding and border.

## What does `box-sizing: border-box` mean?

With **border-box**, the width you set includes padding and border, so a `300px` card really is 300px wide.

```css
.card { box-sizing: border-box; width: 300px; padding: 20px; }   /* still 300px wide */
```

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

Updated: September 27, 2026

Source: https://www.ask-codey.com/glossary/border-box