Left Right Double Arrow (⇔) is the Arrows-block character at Unicode U+21D4 (LEFT RIGHT DOUBLE ARROW). It is a thick bidirectional arrow often used for equivalence or logical iff.
Remember
Character ⇔
Unicode U+21D4
Hex entity ⇔
Decimal ⇔
Named entity ⇔ · ⇔
CSS escape \21D4
Not the same ↔ (↔) · ⇎ (⇎)
All of these produce the same glyph: ⇔. Prefer ⇔ or ⇔ when you want an explicit entity.
Using Hex Code: ⇔
Using HTML Code: ⇔
Using Named Entity: ⇔
Using CSS Entity: ⇔
P ⇔ Q
How It Works
1. Hex:U+21D4 → ⇔ in HTML. The browser turns it into ⇔.
2. Decimal: same code point as 8660 → ⇔. Same result as hex.
3. Named:⇔ and ⇔ are the HTML5 names for this character. Capital A in ⇔ is required — ↔ is a different symbol.
4. CSS: use \21D4 in content (not an HTML entity). #point::after appends that ⇔ after the paragraph text.
Pitfalls & Tips
Common mistakes when working with Left Right Double Arrow.
Look-alikes
⇔ ≠ ↔ ≠ ⇎
⇔ (double), ↔ (single), and ⇎ (stroked double) are different characters.
Case
⇔ ≠ ↔
Named entities are case-sensitive. Capital A selects the double arrow.
Fonts
Glyph may be missing
Arrows-block coverage is usually good, but still test on your target devices.
CSS vs HTML
Do not mix escapes
\21D4 belongs in CSS. ⇔ / ⇔ / ⇔ belong in HTML.
A11y
Add nearby words
Pair the glyph with relation text (for example P ⇔ Q) or use aria-label when it stands alone.
Semicolon
End references
Always finish with ; — write ⇔, not &hArr.
Compatibility
Browser Support
Left Right Double Arrow (U+21D4) and its entity forms (⇔, ⇔, ⇔, ⇔, CSS \\21D4) are supported in all modern browsers. Glyph coverage depends on the font.
✓ Universal encoding
Left Right Double Arrow (⇔)
Encode with named, hex, decimal, or CSS escape — or type ⇔ directly in UTF-8 HTML.
100%Browser coverage
Google ChromeSupported
Yes
Microsoft EdgeSupported
Yes
Mozilla FirefoxSupported
Yes
Apple SafariSupported
Yes
OperaSupported
Yes
Internet ExplorerIE 9+
Yes*
U+21D4 / ⇔Full support
Bottom line: Prefer ⇔ or ⇔ for readable HTML. Use \\21D4 only inside CSS content.
Remember
Key Takeaways
Unicode: this symbol is U+21D4 (decimal 8660).
HTML: prefer ⇔ / ⇔ — or use ⇔ / ⇔.
Use ⇔ or ⇔ (named), ⇔ (hex), ⇔ (decimal), or the CSS escape \21D4 in the content property. You can also type ⇔ directly in UTF-8 HTML.
U+21D4 (LEFT RIGHT DOUBLE ARROW). Hex 21D4, decimal 8660. It belongs to the Arrows block (U+2190–U+21FF).
Yes. ⇔ and ⇔ are both HTML5 named entities. You can also use ⇔ or ⇔.
Use it for equivalence, logical if-and-only-if (iff), and strong bidirectional relations. Prefer ⇔ or ⇔ for readable HTML.
HTML entities (⇔, ⇔, or ⇔) go in markup. The CSS escape \21D4 is used in stylesheets (usually in the content property of ::before/::after). Both render ⇔.
↔ (U+2194) is the single left-right arrow. ⇎ (U+21CE) is the double left-right arrow with a stroke. ⇔ (U+21D4) is the plain double left-right arrow. Named entities are case-sensitive.
🤔
Did you know?
Left Right Double Arrow is Unicode U+21D4 (decimal 8660) — LEFT RIGHT DOUBLE ARROW. HTML5 provides ⇔ and ⇔. Prefer a named form for readable source. Case matters: ⇔ (double) ≠ ↔ (single, U+2194). Do not confuse it with the stroked form ⇎ (U+21CE).
