border-box vs content-box

Written byPhuoc Nguyen

Category

CSS

Created

03 Sep, 2020

`border-box` and `content-box` are two values of the `box-sizing` property. Unlike the `content-box`, the `border-box` value indicates that the dimension of an element will also include the border and padding.

Let's assume that we have a div element whose size is `200px x 100px`, the border and padding are `5px` and `10px` respectively.

.div {
    width: 200px;
    border: 5px;
    padding: 10px;
}

In the content box model, the content inside of element will have the same dimension as the element.

.div {
    /* ... */
    box-sizing: content-box;
}

// Content box
                    ◀︎──── 200px ────▶︎

┌───────────────────────────────────────────────────────┐
|                                                       |
|       ┌───────────────────────────────────────┐       |
|       |                                       |       |
|       |           ┌───────────────┐           |       |
| Border|  Padding  |    Content    |           |       |
|       |           |               |           |       |
|  5px  |    10px   |     200px     |   10px    |  5px  |
|◀︎─────▶︎|◀︎─────────▶︎|◀︎─────────────▶︎|◀︎─────────▶︎|◀︎─────▶︎|
|       |           |               |           |       |
|       |           └───────────────┘           |       |
|       |                                       |       |
|       └───────────────────────────────────────┘       |
|                                                       |
└───────────────────────────────────────────────────────┘

In the border box model, the content's dimension has to subtract the border and padding from the element's dimension. Specifically, the content's width is `200 - 5 * 2 - 10 * 2 = 170px`.

// Border box
◀︎──────────────────────── 200px ────────────────────────▶︎

┌───────────────────────────────────────────────────────┐
|                                                       |
|       ┌───────────────────────────────────────┐       |
|       |                                       |       |
|       |           ┌───────────────┐           |       |
| Border|  Padding  |    Content    |           |       |
|       |           |               |           |       |
|  5px  |    10px   |     170px     |   10px    |  5px  |
|◀︎─────▶︎|◀︎─────────▶︎|◀︎─────────────▶︎|◀︎─────────▶︎|◀︎─────▶︎|
|       |           |               |           |       |
|       |           └───────────────┘           |       |
|       |                                       |       |
|       └───────────────────────────────────────┘       |
|                                                       |
└───────────────────────────────────────────────────────┘

#See also

margin vs padding

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Phước Nguyễn

border-box vs content-box

#See also

Questions? 🙋

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