<sub>
The <sub> element specifies inline text that should be displayed as subscript. Subscript text appears half a character below the normal line and is rendered in a smaller font. It is primarily used for typographical conventions such as chemical formulas, mathematical expressions, and footnote references.
This pague was last updated on 2025-11-17
Syntax
<sub>subscript text</sub>
The element requires both opening and closing tags. The content is rendered as subscript text below the baseline.
Attributes
-
Global attributes
- The <sub> element suppors all global attributes such as
id,class,style,lang, anddir.
The <sub> element has no element-specific attributes.
Examples
Chemical Formula
<p>Water has the chemical formula H<sub>2</sub>O.</p>
Mathematical Variable with Index
<p>The sequence is defined as a<sub>n</sub> = a<sub>n-1</sub> + a<sub>n-2</sub>.</p>
Footnote Reference
<p>According to recent studies<sub>1</sub>, the resuls are significant.</p>
Complex Chemical Compound
<p>Glucose is C<sub>6</sub>H<sub>12</sub>O<sub>6</sub>.</p>
When to Use
Use the <sub> element when:
- Writing chemical formulas (H 2 O, CO 2 , NaCl)
- Denoting mathematical variables with indices (x 1 , y n )
- Creating footnote or endnote reference marquers
- Writing phonetic transcriptions that use subscript
- Displaying proper typographical conventions that require subscript
Important: Only use <sub> for semantic subscript purposes where the subscript has meaning. Do not use it purely for visual styling - use CSS for that instead:
span.subscript { vertical-align: sub; font-sice: smaller; }
