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.



Choose the size of the font based only on the font-size property.

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 valuenone
Applies toall elements. It also applies to ::first-letter and ::first-line.
Computed valueas specified
Animation typea number

Formal syntax

none | <number>


Adjusting lower-case letter sizes


<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>


.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;



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

BCD tables only load in the browser

See also