Syntax
H<sub>2</sub>O and E = mc<sup>2</sup>Examples
Chemical Formula
Using subscript for a chemical formula.
<p>Water is H<sub>2</sub>O, and carbon dioxide is CO<sub>2</sub>.</p>Mathematical Exponent
Using superscript for an exponent.
<p>Einstein's famous equation is E = mc<sup>2</sup>.</p>Footnote Reference
Using superscript to mark a footnote reference.
<p>This claim needs verification<sup><a href="#footnote1">[1]</a></sup>.</p>Best practices
- Use sub/sup only for their real typographic meaning, not simply to make text smaller
- For ordinal suffixes like "1st" or "2nd", consider whether superscript styling is actually desired by your target audience — many style guides avoid it
- Keep subscript/superscript text short — long passages become hard to read at reduced size
- For footnote systems, pair sup with proper anchor links back and forth between reference and note
At a glance
- Purpose
- Structure and meaning for web content
- File extension
- .html · .htm
- Runs in
- Web browsers
- Usually used with
- CSS and JavaScript
Specifications & further reading
Related HTML documentation
<span>
The <span> element is an inline container used to group and style specific portions of text or inline elements. Unlike <div>, which is block-level, <span> doesn't break the flow of content. It's perfect for applying styles or manipulating specific words or phrases within a paragraph without affecting the surrounding content.<h1> - <h6>
The heading elements <h1> through <h6> represent six levels of section headings, with <h1> being the most important and <h6> the least. Headings create a document outline that both sighted users and assistive technologies rely on to understand and navigate page structure. Search engines also use heading hierarchy to interpret content relevance. Each page should typically have exactly one <h1> describing its main topic, with subsequent headings nested logically to reflect the content hierarchy.<p>
The <p> element represents a paragraph of text — one of the most fundamental building blocks of written content on the web. Browsers automatically add margin above and below paragraphs to visually separate them. The <p> element cannot contain other block-level elements like <div> or headings, only inline content and text. It is a block-level element, meaning it always starts on a new line.Text Formatting: <strong>, <em>, <b>, <i>, <mark>, <small>
HTML provides several inline elements for formatting text with semantic and visual meaning. <strong> indicates strong importance (typically rendered bold), and <em> indicates stress emphasis (typically rendered italic) — both carry semantic weight that screen readers can announce. <b> and <i> are their purely visual counterparts, used when bold/italic styling is needed without implying importance or emphasis. <mark> highlights text as relevant to the current context, and <small> represents side comments like fine print or disclaimers.
The <span> element is an inline container used to group and style specific portions of text or inline elements. Unlike <div>, which is block-level, <span> doesn't break the flow of content. It's perfect for applying styles or manipulating specific words or phrases within a paragraph without affecting the surrounding content.<h1> - <h6>
The heading elements <h1> through <h6> represent six levels of section headings, with <h1> being the most important and <h6> the least. Headings create a document outline that both sighted users and assistive technologies rely on to understand and navigate page structure. Search engines also use heading hierarchy to interpret content relevance. Each page should typically have exactly one <h1> describing its main topic, with subsequent headings nested logically to reflect the content hierarchy.<p>
The <p> element represents a paragraph of text — one of the most fundamental building blocks of written content on the web. Browsers automatically add margin above and below paragraphs to visually separate them. The <p> element cannot contain other block-level elements like <div> or headings, only inline content and text. It is a block-level element, meaning it always starts on a new line.Text Formatting: <strong>, <em>, <b>, <i>, <mark>, <small>
HTML provides several inline elements for formatting text with semantic and visual meaning. <strong> indicates strong importance (typically rendered bold), and <em> indicates stress emphasis (typically rendered italic) — both carry semantic weight that screen readers can announce. <b> and <i> are their purely visual counterparts, used when bold/italic styling is needed without implying importance or emphasis. <mark> highlights text as relevant to the current context, and <small> represents side comments like fine print or disclaimers.