CSS width

<!doctype html>
<title>Example</title>
<style>
div {
  background: gold;
  width: 200px;
  height: 150px;
  padding: 20px;
  font-size: 1.5em;
}
</style>
<div>
  How wide am I?
</div>

The CSS width property is used to specify the width of an element.

More specifically, the width property sets the width of the content area or border area (depending on the value of the box-sizing property) of certain boxes.

You can use a length or percentage to specify the width, or you can use one of the keywords.

Also see the max-width, height, and max-height properties.

Syntax

Possible Values

length: Specifies a length value for the width (for example 300px). Negative values are illegal.
percentage: Specifies a percentage value for the width (for example 80%). This is calculated as a width of the generated box's containing block. Negative values are illegal.
available: Equal to the containing block width minus the current element's margin, border, and padding.
max-content: The max-content width.
min-content: The min-content width.
fit-content: Equal to max(min-content, min(max-content, available)).
fit-content(length-percentage): If specified for the inline axis, uses min(max-content size, max(min-content size, length-percentage)); otherwise computes to auto.
auto: The width depends on the values of other properties. The browser will calculate the width accordingly.
stretch: Uses stretch-fit inline size or stretch-fit block size, as appropriate to the writing mode.

In addition, all CSS properties also accept the following CSS-wide keyword values as the sole component of their property value:

initial: Represents the value specified as the property's initial value.
inherit: Represents the computed value of the property on the element's parent.
unset: This value acts as either inherit or initial, depending on whether the property is inherited or not. In other words, it sets all properties to their parent value if they are inheritable or to their initial value if not inheritable.

General Information

Initial Value: auto
Applies To: All except for table rows, row groups, and non-replaced inline elements.
Inherited?: No
Media: Visual
Animatable: Yes (see example)

Example Code

Here are some examples of valid widths:

Official Specifications

CSS basic box model (W3C Editor's Draft)
CSS Intrinsic & Extrinsic Sizing Module Level 3 (W3C Working Draft)
CSS Level 2.1 (W3C Recommendation 07 June 2011)
CSS Level 1 (W3C Recommendation 17 Dec 1996)