The percent sign % (sometimes per cent sign in British English) is the symbol used to indicate a percentage, a number or ratio as a fraction of 100. Related signs include the permille (per thousand) sign ‰ and the permyriad (per ten thousand) sign ‱ (also known as a basis point), which indicate that a number is divided by one thousand or ten thousand, respectively. Higher proportions use parts-per notation.

Correct style

Form and spacing

English style guides prescribe writing the percent sign following the number without any space between (e.g. 50%). However, the International System of Units and ISO 31-0 standard prescribe a space between the number and percent sign, in line with the general practice of using a non-breaking space between a numerical value and its corresponding unit of measurement. Other languages have other rules for spacing in front of the percent sign:

Usage in text

It is often recommended that the percent sign only be used in tables and other places with space restrictions. In running text, it should be spelled out as percent or per cent (often in newspapers). For example, not "Sales increased by 24% over 2006" but "Sales increased by 24 percent over 2006".

Evolution

Prior to 1425, there is no known evidence of a special symbol being used for percentages. The Italian term per cento, "for a hundred", was used as well as several different abbreviations (e.g. "per 100", "p 100", "p cento"). Examples of this can be seen in the 1339 arithmetic text (author unknown) depicted below. The letter p with its descender crossed by a horizontal or diagonal stroke (to indicate abbreviation) conventionally stood for per, por, par, or pur in Medieval and Renaissance palaeography. At some point, a scribe used the abbreviation pc with a tiny loop or circle (depicting the ending -o used in Italian ordinals, as in primo, secondo; it is analogous to the English -th as in 25th). This appears in some additional pages of a 1425 text which were probably added around 1435. The pc with a loop eventually evolved into a horizontal fraction sign by 1650 (see below for an example in a 1684 text) and thereafter lost the per. In 1925, D. E. Smith wrote, "The solidus form is modern."

Encodings

Unicode

The Unicode code points are:

ASCII

The ASCII code for the percent character is 37, or 0x25 in hexadecimal.

Other uses

In computers

Names for the percent sign include percent sign (in ITU-T), mod, grapes (in hacker jargon), and the humorous double-oh-seven (in INTERCAL). In computing, the percent character is also used for the modulo operation in programming languages that derive their syntax from the C programming language, which in turn acquired this usage from the earlier B. In the textual representation of URIs, a % immediately followed by a 2-digit hexadecimal number denotes an octet specifying (part of) a character that might otherwise not be allowed in URIs (see percent-encoding). In SQL, the percent sign is a wildcard character in "LIKE" expressions, for example SELECT * FROM table WHERE fullname LIKE 'Lisa %' will fetch all records whose names start with "Lisa". In TeX (and therefore also in LaTeX) and PostScript, and in GNU Octave and MATLAB, a % denotes a line comment. In BASIC, Visual Basic, ASP, and VBA a trailing % after a variable name marks it as an integer. In ASP, the percent sign can be used to indicate the start and end of the ASP code <%...... %> In Perl % is the sigil for hashes. In many programming languages' string formatting operations (performed by functions such as and ), the percent sign denotes parts of the template string that will be replaced with arguments. (See printf format string.) In Python and Ruby the percent sign is also used as the string formatting operator. In the command processors COMMAND.COM (DOS) and CMD.EXE (OS/2 and Windows), %1, %2,... stand for the first, second,... parameters of a batch file. %0 stands for the specification of the batch file itself as typed on the command line. The % sign is also used similarly in the FOR command. %VAR1% represents the value of an environment variable named VAR1. Thus: set PATH=c:;%PATH% sets a new value for PATH, that being the old value preceded by " ". Because these uses give the percent sign special meaning, the sequence %% (two percent signs) is used to represent a literal percent sign, so that: set PATH=c:;%%PATH%% would set PATH to the literal value " ". In the C Shell, % is part of the default command prompt.

In linguistics

In linguistics, the percent sign is prepended to an example sentence or other string to show that it is judged well-formed (grammatical) by some speakers and ill-formed by others. This may be due to differences in dialect or even individual idiolects. This use is similar to those of the asterisk to mark ill-formed strings, the question mark to mark strings where well-formedness is unclear, and the number sign to mark strings that are syntactically well-formed but semantically or pragmatically nonsensical.

Sources