Uppercase H double struck (ℍ) is the Unicode character at U+210D in Letterlike Symbols. Official name: DOUBLE-STRUCK CAPITAL H — a blackboard-bold H used in mathematical notation, most often for the set of quaternions.
Remember
Character ℍ
Unicode U+210D
Named entity ℍ
Hex entity ℍ
Decimal ℍ
CSS escape \210D
Not the same H · Ĥ · ℂ
Prefer ℍ in HTML markup. Numeric forms and typing ℍ in UTF-8 also work. Use a math-capable font when the blackboard-bold shape matters.
Using Named Entity: ℍ
Using Hex Code: ℍ
Using HTML Code: ℍ
Using CSS Entity: ℍ
Typed directly: ℍ
Quaternions: q ∈ ℍ
How It Works
1. Named:ℍ is the clearest HTML form for U+210D (from “Hopf” / blackboard-bold letter naming).
2. Hex:U+210D → ℍ in HTML. Same glyph as the named entity.
3. Decimal: same code point as 8461 → ℍ. Same glyph as hex and named.
4. CSS: use \210D in content (not an HTML entity). #point::after appends that ℍ after the paragraph text.
5. Typed / math: paste ℍ in UTF-8, or write q ∈ ℍ for a short membership label.
Pitfalls & Tips
Common mistakes when working with U+210D.
vs H
Not a plain capital H
ASCII H (U+0048) is not letterlike. Use ℍ when you need the double-struck quaternion symbol.
vs Ĥ
Not H with circumflex
Ĥ (Ĥ) is an accented letter. ℍ is a mathematical letterlike symbol.
vs bold
Not CSS bold
font-weight: bold only thickens a letter. U+210D is a dedicated double-struck character.
Fonts
Letterlike coverage varies
Some fonts fall back to a plain H. Prefer Cambria Math, STIX, or another math font for ℍ.
CSS vs HTML
Do not mix escapes
\210D belongs in CSS strings. ℍ / ℍ / ℍ belong in HTML.
Math
Mark math context
For formulas, wrap math in appropriate markup (for example MathML or a math role) so assistive tech can treat it as math.
Compatibility
Browser Support
Double-struck capital H (U+210D) and its entity forms (ℍ, ℍ, ℍ, CSS \\210D) are supported in all mainstream browsers. Visible glyphs depend on Letterlike Symbols font coverage.
✓ Universal support
Uppercase H Double Struck (ℍ)
Encode with named, hex, decimal, CSS escape, or type the character — same code point everywhere encoding is supported.
100%Browser coverage
Google ChromeSupported
Yes
Microsoft EdgeSupported
Yes
Mozilla FirefoxSupported
Yes
Apple SafariSupported
Yes
OperaSupported
Yes
Internet ExplorerIE 9+
Yes
U+210D / ℍFull support
Bottom line: Prefer ℍ in HTML. Use \\210D only inside CSS content. Do not confuse with plain H or Ĥ (Ĥ).
Remember
Key Takeaways
Unicode: double-struck H is U+210D (decimal 8461) — glyph ℍ.
HTML: prefer ℍ — also ℍ / ℍ.
CSS: use \210D inside content for generated text.
Meaning:ℍ is quaternions / blackboard bold — not plain H, not Ĥ.
Use ℍ (named), ℍ (hex), ℍ (decimal), type ℍ directly in UTF-8, or the CSS escape \210D in content. Prefer ℍ in normal HTML.
U+210D (DOUBLE-STRUCK CAPITAL H). Hex 210D, decimal 8461. It belongs to Letterlike Symbols (U+2100–U+214F).
Yes. Use ℍ. Numeric forms ℍ and ℍ also work.
No. ℍ is double-struck capital H (U+210D, ℍ). Plain H is U+0048. Ĥ is H with circumflex (Ĥ, U+0124).
Use it in mathematical notation for the quaternions (for example q ∈ ℍ), or whenever blackboard-bold H is required — not as a substitute for plain H.
HTML entities (ℍ, ℍ, or ℍ) go in markup. The CSS escape \210D goes in stylesheet strings (usually content on ::before/::after).
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Did you know?
Double-struck capital H is Unicode U+210D (decimal 8461) — glyph ℍ in Letterlike Symbols (U+2100–U+214F). HTML5 names it ℍ. Official name: DOUBLE-STRUCK CAPITAL H. In mathematics it usually denotes the quaternions. Prefer a math-capable font for the blackboard-bold look.
