If you have ever written 5' 10" for a height, you used the wrong characters. Those are a straight quote and a double quote standing in for the prime and the double prime, and the substitution is so universal that most people have never seen the real marks. The shapes genuinely differ — a prime is a slanted stroke, a quote curls — which is why Butterick's Practical Typography devotes an entire page to the error.
The mark earns its keep across fields with nothing else in common. It is arcminutes in astronomy, and arcseconds when doubled. It is feet and inches, per Unicode's own annotation. In calculus it marks the derivative, f′(x), a notation Lagrange put into circulation in his Théorie des fonctions analytiques of 1797. Geometry uses it for transformed points, so a rotated (x, y) becomes (x′, y′). Molecular biology reads DNA from the 5′ end to the 3′ end, where the primes are naming carbon positions on a sugar ring.
The confusion runs in both directions, which is the joke. Unicode considers the curly right single quotation mark the correct character for an apostrophe — yet people type a straight one there, then turn around and use quote marks where actual primes belong. Autocorrect compounds it by curling the mark, carrying it further still from the upright stroke that feet and inches want.
About Prime
Prime is the Unicode character ′ at codepoint U+2032 in the General Punctuation block of the Basic Multilingual Plane (BMP).
Technical Reference
| Unicode Codepoint | |
| Decimal | |
| UTF-8 (hex) | |
| UTF-16 (hex) | |
| HEX Entity | |
| HTML Entity | |
| CSS (\xxxx) | |
| JavaScript | |
| Python |
How to Use Prime
To use the Prime symbol (′) in HTML, insert the
entity ′ directly into your markup. The decimal entity ′ works in any HTML-serialised document.
In CSS pseudo-elements use content: '\2032';.
In JavaScript and TypeScript the escape '\u2032' evaluates to ′. In Python source, write '\u2032'.
The character encodes to E2 80 B2 as UTF-8 bytes and 2032 as UTF-16 code units. Its decimal codepoint is 8242.
This is a text-based Unicode character. It will render in the current font on most platforms. If a font lacks this glyph, the browser may show a placeholder or fall back to a system font.