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font-size-adjust

The font-size-adjust CSS property sets the size of lower-case letters relative to the current font size (which defines the size of upper-case letters).

/* Use the specified font size */
font-size-adjust: none;

/* Use a font size that makes lowercase
   letters half the specified font size */
font-size-adjust: 0.5;

/* Global values */
font-size-adjust: inherit;
font-size-adjust: initial;
font-size-adjust: unset;

The property is useful since the legibility of fonts, especially at small sizes, is determined more by the size of lowercase letters than by the size of capital letters. Legibility can become an issue when the first-choice font-family is unavailable and its replacement has a significantly different aspect ratio (the ratio of the size of lowercase letters to the size of the font).

To use this property in a way that is compatible with browsers that do not support font-size-adjust, it is specified as a number that the font-size property is multiplied by. This means the value specified for the property should generally be the aspect ratio of the first choice font. For example, a style sheet that specifies:

font-size: 14px;  
font-size-adjust: 0.5;

... is really specifying that the lowercase letters of the font should be 7px high (0.5 × 14px). This will still produce reasonable results in browsers that do not support font-size-adjust, where a 14px font will be used.

Syntax

Values

none
Choose the size of the font based only on the font-size property.
<number>

Choose the size of the font so that its lowercase letters (as determined by the x-height of the font) are the specified number times the font-size.

The number specified should generally be the aspect ratio (ratio of x-height to font size) of the first choice font-family. This means that the first-choice font, when available, will appear the same size in browsers, whether or not they support font-size-adjust.

0 yields text of zero height (hidden text).

Formal definition

Initial value none
Applies to all elements. It also applies to ::first-letter and ::first-line.
Inherited yes
Computed value as specified
Animation type a number

Formal syntax

none | <number>

Examples

Adjusting lower-case letter sizes

HTML

<p class="times">This text uses the Times font (10px), which is hard to read in small sizes.</p>
<p class="verdana">This text uses the Verdana font (10px), which has relatively large lowercase letters.</p>
<p class="adjtimes">This is the 10px Times, but now adjusted to the same aspect ratio as the Verdana.</p>

CSS

.times {
  font-family: Times, serif;
  font-size: 10px;
}

.verdana {
  font-family: Verdana, sans-serif;
  font-size: 10px;
}

.adjtimes {
  font-family: Times, serif; 
  font-size-adjust: 0.58;
  font-size: 10px;
}

Results

Specifications

Specification Status Comment
CSS Fonts Module Level 3
The definition of 'font-size-adjust' in that specification.
Candidate Recommendation Initial definition

The CSS property font-size-adjust was initially defined in CSS 2, but dropped in CSS 2.1. It has been newly defined in CSS 3.

Browser compatibilityUpdate compatibility data on GitHub

Desktop
Chrome Edge Firefox Internet Explorer Opera Safari
font-size-adjust 43
Disabled
43
Disabled
Disabled From version 43: this feature is behind the Enable experimental Web Platform features preference. To change preferences in Chrome, visit chrome://flags.
79
Disabled
79
Disabled
Disabled From version 79: this feature is behind the Enable experimental Web Platform features preference.
40
40
3
Before Firefox 40, font-size-adjust: 0 was incorrectly interpreted as font-size-adjust: none (bug 1144885).
1
Before Firefox 3, font-size-adjust was supported on Windows only.
No 30
Disabled
30
Disabled
Disabled From version 30: this feature is behind the Enable experimental Web Platform features preference.
No
Mobile
Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet
font-size-adjust No 43
Disabled
43
Disabled
Disabled From version 43: this feature is behind the Enable experimental Web Platform features preference. To change preferences in Chrome, visit chrome://flags.
4 30
Disabled
30
Disabled
Disabled From version 30: this feature is behind the Enable experimental Web Platform features preference.
No No

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https://developer.mozilla.org/en-US/docs/Web/CSS/font-size-adjust