CSS Width A Comprehensive Guide for Web Design

Discover the CSS width property, its use cases, and available options.

Learn how to set element widths using pixels, ems, and percentages.

Create responsive designs.

The width property in CSS sets how wide an element is. It can be the content area or the border area, depending on the box-sizing property. This property is crucial for creating responsive designs that look good on different devices and screen sizes.

How `width` Works

Default Behavior: By default, width sets the width of the content area. If box-sizing is set to border-box, it sets the width of the border area.
Constraints: The width property is subject to min-width and max-width. If width is less than min-width, min-width takes over. If width is greater than max-width, max-width takes over.
SVG Elements: width also applies to SVG elements like <svg>, <rect>, <image>, and <foreignObject>. For instance, auto resolves to 100% for <svg> and 0 for other elements, and percent values are relative to the SVG viewport width for <rect>.

Example

Here’s a simple example to demonstrate the use of the width property:

<!DOCTYPE html>
<html>
<head>
    <title>CSS width Property</title>
    <style>
        .auto-width {
            width: auto;
            color: white;
            font-size: 20px;
            background-color: rgb(0, 150, 0);
        }
        h2 {
            font-size: 20px;
            color: black;
        }
    </style>
</head>
<body>
    <h2>CSS width Property</h2>
    <p class="auto-width">
        This is an example of the auto width property.
    </p>
</body>
</html>

In this example, the paragraph with the class auto-width will have its width automatically calculated by the browser, making it flexible and adaptive to different content and screen sizes.

Using `initial`

The width: initial property sets an element’s width to its default value. This resets the width to its original state, ignoring any previously applied width styles.

<!DOCTYPE html>
<html>
<head>
    <title>CSS width Property</title>
    <style>
        .initial-width {
            width: initial;
            color: white;
            font-size: 20px;
            background-color: rgb(0, 150, 0);
        }
        h2 {
            font-size: 20px;
            color: black;
        }
    </style>
</head>
<body>
    <h2>CSS width Property</h2>
    <p class="initial-width">
        This is an example of the initial width property.
    </p>
</body>
</html>

Units: Pixels and Ems

You can set the width of an element using pixels (px) and ems (em). Pixels are fixed, while ems are relative to the font size.

.px-width {
  width: 200px;
  background-color: red;
  color: white;
  border: 1px solid black;
}

.em-width {
  width: 20em;
  background-color: white;
  color: red;
  border: 1px solid black;
}

Example using max-content

The max-content value sets the width of an element to its intrinsic preferred width.

p.max-content {
  background: lightgreen;
  width: max-content;
}

And the HTML:

<p class="max-content">The MDN community writes really great documentation.</p>

Formal Definition

Initial Value: auto. The browser calculates the width based on content and available space.
Applies To: All elements except non-replaced inline elements, table rows, and row groups.
Inherited: No.
Percentages: Relative to the width of the containing block.
Computed Value: Can be a percentage, auto, or an absolute length.
Animation Type: Can be animated using length, percentage, or calc() values.

Specifications

The width property is defined by the CSS Box Sizing Module Level 4 and the CSS Sizing Module Level 4.

[The box model]WebsiteUrl: Learn about the CSS box model.
[height]WebsiteUrl: Explore the height property.
[box-sizing]WebsiteUrl: Understand how box-sizing affects the calculation of an element’s width and height.
[min-width]WebsiteUrl and [max-width]WebsiteUrl: Set minimum and maximum width constraints.
[Mapped logical properties: block-size and inline-size]WebsiteUrl: More flexible control of element dimensions.
[anchor-size()]WebsiteUrl: Set the size of an element relative to an anchor element.