Several MathML presentation elements have attributes that accept length values used for size or spacing. MathML accepts different units and constants for specifying lengths.


Unit Description
em font-relative unit
ex font-relative unit. (The "x"-height of the element, 1ex ≈ 0.5em in many fonts)
px Pixels
in Inches (1 inch = 2.54 centimeters)
cm Centimeters
mm Millimeters
pt Points (1 point = 1/72 inch)
pc Picas (1 pica = 12 points)
% Percentage of the default value.


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.

A replacement for the deprecated constants below is:

veryverythinmathspace  => 0.05555555555555555em
verythinmathspace      => 0.1111111111111111em
thinmathspace          => 0.16666666666666666em
mediummathspace        => 0.2222222222222222em
thickmathspace         => 0.2777777777777778em
verythickmathspace     => 0.3333333333333333em
veryverythickmathspace => 0.3888888888888889em
Constant Value
veryverythinmathspace 1/18em
verythinmathspace 2/18em
thinmathspace 3/18em
mediummathspace 4/18em
thickmathspace 5/18em
verythickmathspace 6/18em
veryverythickmathspace 7/18em
Negative contstants are introduced in Gecko 7.0 (Firefox 7.0 / Thunderbird 7.0 / SeaMonkey 2.4) (bug 650530)
negativeveryverythinmathspace -1/18em
negativeverythinmathspace -2/18em
negativethinmathspace -3/18em
negativemediummathspace -4/18em
negativethickmathspace -5/18em
negativeverythickmathspace -6/18em
negativeveryverythickmathspace -7/18em

Note: Namedspace binding is deprecated in MathML3 and has been removed in Gecko 15.0 (Firefox 15.0 / Thunderbird 15.0 / SeaMonkey 2.12) (bug 673759).