Deprecated: This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.

The mathsize global attribute sets the font-size of a MathML element.

Note: Use CSS for styling MathML whenever possible. The mathsize attribute should only be included for applications that are not CSS-aware and will be overridden by the CSS font-size property, if set.


<!-- <length> values -->
<math mathsize="12px">
<math mathsize="0.8em">

<!-- <percentage> values -->
<math mathsize="80%">



A positive <length> value. For most font-relative units (such as em and ex), the font size is relative to the parent element's font size.


A positive <percentage> value, relative to the parent element's font size.

Note: Some browsers may also accept legacy MathML lengths.


MathML Core
# dfn-mathsize
  • In MathML 3 and earlier versions, keywords small, normal, and big as well as the MathML3-specific syntax for lengths was supported. Since MathML Core, the syntax matches CSS <length-percentage> values.
  • This attribute was designed for MathML applications that are not CSS-aware. Since MathML Core, the use of equivalent CSS is recommended instead.

Browser compatibility

BCD tables only load in the browser

See also