In typography, the point is the smallest unit of measure. It is used for measuring font size, leading, and other items on a printed page. The size of the point has varied throughout printing's history. Since the 18th century, the size of a point has been between 0.18 and 0.4 millimeters. Following the advent of desktop publishing in the 1980s and 1990s, digital printing has largely supplanted the letterpress printing and has established the desktop publishing (DTP) point as the de facto standard. The DTP point is defined as of an international inch and, as with earlier American point sizes, is considered to be of a pica.
In metal type, the point size of the font describes the height of the metal body on which the typeface's characters were cast. In digital type, letters of a font are designed around an imaginary space called an em square. When a point size of a font is specified, the font is scaled so that its em square has a side length of that particular length in points. Although the letters of a font usually fit within the font's em square, there is not necessarily any size relationship between the two, so the point size does not necessarily correspond to any measurement of the size of the letters on the printed page.
History
The point was first established by the Milanese typographer, Francesco Torniella da Novara ( – 1589) in his 1517 alphabet, L'Alfabeto. The construction of the alphabet is the first based on logical measurement called "Punto," which corresponds to the ninth part of the height of the letters or the thickness of the principal stroke.
Notations
A measurement in points can be represented in three different ways. For example, 14 points (1 pica plus 2 points) can be written:
(12 points would be just "")—traditional style
1p2 (12 points would be just "1p")—format for desktop
14pt (12 points would be "12pt" or "1pc" since it is the same as 1 pica)—format used by Cascading Style Sheets defined by the World Wide Web Consortium.
Varying standards
There have been many definitions of a "point" since the advent of typography. Traditional continental European points at about are usually a bit larger than English points at around .
French points
The Truchet point, the first modern typographic point, was of a French inch or of the royal foot. It was invented by the French clergyman Sébastien Truchet. During the metrication of France amid its revolution, a 1799 law declared the meter to be exactly 443.296 French lines long. This established a length to the royal foot of m or about 325 mm. The Truchet point therefore became equal to mm or about . It has also been cited as exactly 0.188 mm.
The Fournier point was established by Pierre Simon Fournier in 1737. The system of Fournier was based on a different French foot of c. 298 mm. With the usual convention that 1 foot equals 12 inches, 1 inch (pouce) was divided into 12 lines (lignes) and 1 line was further divided into 6 typographic points (points typographiques). One Fournier point is about 0.0135 English inches.
Fournier printed a reference scale of 144 points over two inches; however, it was too rough to accurately measure a single point.
The Fournier point did not achieve lasting popularity despite being revived by the Monotype Corporation in 1927. It was still a standard in Belgium, in parts of Austria, and in Northern France at the beginning of the 20th century. In Belgium, the Fournier system was used until the 1970s and later. It was called the "mediaan"-system.
The Didot point, established by François-Ambroise Didot in 1783, was an attempt to improve the Fournier system. He did not change the subdivisions (1 inch = 12 subdivisions = 72 points), but defined it strictly in terms of the royal foot, a legal length measure in France: the Didot point is exactly of a French foot or of a French inch, that is (by 1799) mm or about . Accordingly, one Didot point is exactly two Truchet points.
However, 12 Fournier points turned out to be 11 Didot points, giving a Fournier point of about ; later sources state it as being . To avoid confusion between the new and the old sizes, Didot also rejected the traditional names, thus parisienne became corps 5, nonpareille became corps 6, and so on. The Didot system prevailed because the French government demanded printing in Didot measurements.
Approximations were subsequently employed, largely owing to the Didot point's unwieldy conversion to metric units (the divisor of its conversion ratio has the prime factorization of ).