Maths and technical symbols

Most of this page comes from the Mathematical Operators block at U+2200, a large and orderly range covering comparison, set theory, logic and calculus. A handful of the most used characters are older than the block itself: × ÷ ± ° ¼ ½ ¾ and the superscript digits were inherited from Latin-1, which took them from typewriter and telex conventions, so they are the ones you can rely on absolutely everywhere.

Unicode contains a small number of characters that look identical to each other, and this set has two of the best known examples. µ, the micro sign, and μ, the Greek letter mu, are distinct code points that most fonts draw the same way. Unicode kept both so that documents in older encodings could survive a round trip unchanged. The consequence is real: a search for one may not match the other, and some normalisation processes silently convert between them. The ohm sign and the Greek capital omega have exactly the same relationship, as do the increment sign and a Greek capital delta.

The measurement marks are the ones people most often get wrong. ′ and ″ are primes, and they are the correct characters for feet and inches, and for minutes and seconds of arc, in a way that an apostrophe and a double quote are not. A curly quotation mark leans, a prime is a straight upright stroke, and typing 5′11″ rather than the keyboard substitutes is the difference between notation and improvisation. The degree sign ° has its own set of impostors, including the masculine ordinal indicator, which is a different character that happens to be drawn as a small raised circle.

The large operators ∑ ∏ ∫ ∮ come with a limitation that catches people out. In real typesetting these grow to match the height of whatever they enclose. In plain text they cannot: they are single characters drawn at text size, so a summation over a tall expression will look undersized next to it, and there is no way to attach limits above and below. They are for referring to an operation, not for setting one.

Which is the honest summary of the whole page. These characters are for the places that have no formula editor: a spreadsheet note, a chat message, a commit description, a homework answer typed into a text box, a specification line that needs a tolerance. For anything that has to be read as real mathematics, and especially for anything that has to be accessible to a screen reader, proper notation in LaTeX or MathML carries structure that a row of symbols cannot.

Common questions

Why are there two characters that both look like mu?

Because Unicode encoded the micro sign separately from the Greek letter so that text converted from older character sets would come back unchanged. They look identical in most fonts but are different code points, which means a search for one may not find the other and some systems quietly convert between them.

How do I type feet and inches correctly?

Use the prime characters ′ and ″, not an apostrophe and a double quotation mark. Primes are straight upright strokes designed for exactly this, while typographic quotes curl and lean the wrong way. The same characters are correct for minutes and seconds of arc in coordinates.

Can I write a full equation with these symbols?

Only a simple one on a single line. Plain text cannot stack a numerator over a denominator, size a summation sign to its contents or place limits above and below an integral. For anything more structured, and for anything that needs to be read aloud correctly, use LaTeX or MathML instead.

Why does × look better than the letter x?

Because it is the actual multiplication sign, drawn symmetrically and spaced as an operator, whereas a lowercase x is a letter with letter spacing and often a slight slant. Beyond appearance, using the right character means the text is not mistaken for a word by search or by assistive technology.

See also

• Currency symbols
• Arrow symbols
• Geometric shape symbols
• Punctuation and divider symbols