Square root symbol (√) in HTML
The square root symbol is the radical sign. Its named reference is √ and its code point is U+221A, and it carries no horizontal bar over the expression.
At a glance
- Character
- √
- Named entity
- √
- Decimal reference
- √
- Hex reference
- √
- Unicode code point
- U+221A
- Unicode name
- SQUARE ROOT
- In the entity reference
- Math
In detail
The character is the hook alone. In printed mathematics the hook comes with a vinculum, the horizontal bar that stretches over everything inside the root and defines exactly where it ends. Unicode does not encode a stretchy bar, so the plain character leaves the extent of the radicand entirely undefined and the reader has to guess.
For a single symbol or a short number that is fine. The root of two, or the root of x, is unambiguous. The moment the radicand is a sum, a product or anything with more than one term, parentheses stop being optional: without them the expression reads as the root of the first term followed by the rest, which is a different value.
Cube and fourth roots have their own precomposed characters at U+221B and U+221C. They have no named entities and are not in the entity reference tool's list, so they need numeric references, and they inherit the same missing bar problem. Higher roots have no character at all and must be written as a fractional exponent or in MathML.
Anything a reader actually has to work through belongs in MathML rather than in characters. MathML draws the bar at the correct width automatically, it expresses the nesting so assistive technology can walk the expression, and it survives a change of font size without the pieces drifting apart. Characters are for a formula mentioned in passing, not for a formula being taught.
Examples
<p>√2 ≈ 1.41421</p>
<p>√(a² + b²) is the hypotenuse.</p>Without the brackets the second expression reads as the root of a squared, plus b squared.
<math>
<msqrt>
<mrow>
<msup><mi>a</mi><mn>2</mn></msup>
<mo>+</mo>
<msup><mi>b</mi><mn>2</mn></msup>
</mrow>
</msqrt>
</math>Things that catch people out
- There is no overbar. A multi term radicand written without brackets is ambiguous no matter how it looks in your editor.
- The cube root at U+221B has no named entity, so &cbrt; and similar guesses render as literal text.
- Faking the bar with a CSS top border on a span breaks as soon as the text wraps or the font size changes, and it tells assistive technology nothing.
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