field-sizing

content

Allows the element to adjust its size to fit its contents.

fixed

Sets a fixed size for the element. This is the default value.

field-sizing: content overrides the default preferred sizing of form elements. This setting provides an easy way to configure text inputs to shrinkwrap their content and grow as more text is entered. They stop expanding when they reach maximum size limits (defined by the size of their containing element or set via CSS), at which point scrolling is required to view all the content.

Specifically, field-sizing to content affects the following elements:

• Form input types that accept direct text input from users. This includes email, number, password, search, tel, text, and url types.
  • If no minimum width is set on the control, it will only be as wide as the text cursor.
  • Controls with placeholder attributes will be rendered large enough to display the placeholder text.
  • The size attribute modifies the default preferred size of such <input> elements. As a result, size has no effect on <input> elements with field-sizing: content set.
• file inputs. Direct text input is not possible; however, the displayed filename changes as the user selects a new file to upload. When field-sizing: content is set, the control will change size to shrinkwap the filename.
• <textarea> controls. It is worth noting that <textarea> elements with field-sizing: content set behave much like single-line text controls, with the following additions:
  • If <textarea> elements are unable to grow due to a width constraint, they will start to grow in height to display additional rows of content. When a height constraint is then reached, they will then start to show a scrollbar to allow all the content to be viewed.
  • rows and cols attributes modify the default preferred size of a <textarea>. As a result, rows/cols have no effect on <textarea> elements with field-sizing: content set.
• <select> controls. These behave a bit differently to what you might expect with field-sizing: content set. The effect depends on the type of <select> control you are creating:
  • Regular drop-down boxes will change their width to always fit the displayed option value as new values are selected. (By default, the drop-down's size is set to be large enough to display the longest option value.)
  • List boxes (<select> elements with the multiple or size attribute) will be large enough to display all the options without needing to scroll. (By default, the drop-down box will require scrolling to view all the option values.)
  • The size attribute has very little effect on <select> elements that have field-sizing: content set. In such cases, the browser checks if the size is equal to 1 to determine whether the <select> control should appear as a drop-down or a listbox. However, it will always display all the options of a listbox, even if size is smaller than the number of options.

The sizing flexibility provided to form controls by field-sizing: content can be overridden if you use other CSS sizing properties. Avoid setting a fixed width and height when using field-sizing: content because they will reimpose a fixed size on the control. However, using properties like min-width and max-width alongside field-sizing: content is quite effective because they allow the control to grow and shrink with the entered text and also prevent the control from becoming too large or too small.

The maxlength attribute causes the control to stop growing in size when the maximum character limit is reached.

field-sizing = 
  fixed    |
  content  

This example illustrates the effect of field-sizing: content on single- and multi-line text fields. The fields adjust their size as text is added or removed, effectively shrinkwrapping the contents, until a lower or upper size limit is reached.

HTML

The HTML in this example contains three form fields, each with an associated <label>: two <input> elements of types text and email and a <textarea> element.

<div>
  <label for="name">Enter name:</label>
  <input type="text" id="name" maxlength="50" />
</div>
<div>
  <label for="email">Enter email:</label>
  <input type="email" id="email" maxlength="50" placeholder="e.g. a@b.com" />
</div>
<div>
  <label for="comment">Enter comment:</label>
  <textarea id="comment">This is a comment.</textarea>
</div>

Note the following points about the HTML:

• The first two fields have a maxlength attribute set, which stops the size of the field from increasing when the character limit is reached.
• The <textarea> will grow in the inline direction until the edge of the min-width constraint (set in the CSS code below) is reached, then start to add new lines in the block direction to contain subsequent characters.
• The email input has a placeholder set. This causes the field to render big enough to show the entire placeholder. Once the field is focused and the user starts typing, the field changes size to the min-width value. The text field, which doesn't have a placeholder, renders initially at min-width.

CSS

In the CSS, we set field-sizing: content on the three form fields, along with a min-width and max-width to constrain the input size. It is worth reiterating that, if no minimum width was set on the fields, they would be rendered only as wide as the text cursor.

We also give the <label>s some rudimentary styling so that they sit neatly next to the fields.

body {
  box-sizing: border-box;
  padding: 20px;
}

div {
  margin-bottom: 20px;
  display: flex;
}

input,
textarea {
  field-sizing: content;
  min-width: 50px;
  max-width: 350px;
}

label {
  width: 150px;
  margin-right: 20px;
  text-align: right;
}

Result

Try entering and removing text in the fields below to explore the effects of field-sizing: content alongside other sizing properties.

This example illustrates the effect of field-sizing: content on <select> elements, both drop-down menu types and multiline listbox types.

HTML

The HTML contains two sets of <select> elements: one with field-sizing: content applied, and one without, allowing you to see the difference (though the effect may be less obvious than on text fields). Each set includes one drop-down menu type and one multiline listbox type (with the multiple attribute set).

<div class="field-sizing">
  <h2>With <code>field-sizing: content</code></h2>
  <select>
    <option>Bananas</option>
    <option>Strawberries</option>
    <option selected>Apples</option>
    <option>Raspberries</option>
    <option>Pomegranate</option>
  </select>
  <select multiple>
    <option>Bananas</option>
    <option>Strawberries</option>
    <option>Apples</option>
    <option>Raspberries</option>
    <option>Pomegranate</option>
  </select>
</div>
<div>
  <h2>Without <code>field-sizing: content</code></h2>
  <select>
    <option>Bananas</option>
    <option>Strawberries</option>
    <option selected>Apples</option>
    <option>Raspberries</option>
    <option>Pomegranate</option>
  </select>
  <select multiple>
    <option>Bananas</option>
    <option>Strawberries</option>
    <option>Apples</option>
    <option>Raspberries</option>
    <option>Pomegranate</option>
  </select>
</div>

CSS

In the CSS, field-sizing: content is set only on the first set of <select> elements.

body {
  box-sizing: border-box;
  display: flex;
  gap: 20px;
  font-family: sans-serif;
}

h2 {
  margin-top: 0;
  font-size: 1rem;
  text-align: center;
  flex: 1 0 100%;
}

div {
  margin-bottom: 20px;
  flex: 1;
  display: flex;
  align-items: flex-start;
  justify-content: space-around;
  flex-flow: row wrap;
}

select {
  valign: top;
}

.field-sizing select {
  field-sizing: content;
}

Result

Note the following effects of field-sizing: content:

• The drop-down menu always fits the size of the displayed option, changing size as different options are selected. Without field-sizing: content, the size is fixed as wide as the longest option.
• The multi-select list box displays all of the options at once. Without field-sizing: content, the user has to scroll the box to view all the options.

• <input>
• <select>
• <textarea>