Unit system typographic unit 1 point in ... ... is equal to ... imperial/US units 1/72 in | Unit of length typographic units 1/12 picas metric (SI) units 0.3528 mm | |
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 the history of printing. Since the 18th century, the point's size has varied from 0.18 to 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 DTP point (desktop publishing point) as the de facto standard. The DTP point is defined as 1⁄72 of an international inch (about 0.353 mm) and, as with earlier American point sizes, is considered to be 1⁄12 of a pica.
Contents
- History
- Notations
- Varying standards
- French points
- American points
- Desktop publishing point
- Point size names
- References
In metal type, the point size of the font described 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 (c.1490 – 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:
Varying standards
There have been many definitions of a “point” since the advent of typography. Traditional continental European points at about 375 µm are usually a bit larger than English points at around 350 µm.
French points
The Truchet point, the first modern typographic point, was 1/144 of a French inch or 1/1728 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. At 9000 lines or 16 inches per foot, this established a length to the royal foot of 7003900000000000000♠9000/7004277060000000000♠27706 or ca. 325 mm, which made the Truchet point equal to 7004156250000000000♠15625/7004831180000000000♠83118mm or about 6996187986000000000♠187.986 µm, although it has also been cited as exactly 188 µm.
The Fournier point established by Pierre Simon Fournier was about 11/864 French inches or (by 1799) 345 µm. This is very close to the present international point, but Fournier's point did not achieve lasting popularity despite being revived by the Monotype Corporation in 1927. It became standard in Belgium.
The Didot point established by François-Ambroise Didot in the 18th century was twice Truchet's and thus 1/864 of the royal foot, i.e. by 1799 7004156250000000000♠15625/7004415590000000000♠41559mm or ca. 6996375971000000000♠375.971 µm.
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 3×7×1979.) Values included Hermann Berthold's 376 µm point and Jan Tschichold's 6996375939999999999♠375.94 µm (266 points to 100 mm). Due to the definition in TeX of 1157 dd = 1238 pt, the slightly larger 6996376065000000000♠376.065 µm became a common value.
TeX also supports a new Didot point (nd) at 3/8mm or 375 µm, and cites a 1978 redefinition for it. The French National Print Office adopted a point of 2/5mm or 400 µm exactly and continues to use this measurement today. Japanese and German standardization bodies instead opted for a metric typographic base measure of exactly 1/4mm or 250 µm. It is called Q in Japanese after the initial letter of quarter millimetre. Due to demand by Japanese typesetters, CSS adopted Q in 2015.
The Didot point has been mostly replaced by the DTP point in Europe and throughout the world.
American points
A typographic or printer's foot contains 72 picas or 864 points. The Metric Act of 1866 established a legal ratio of 1200 : 3937 between the foot and the meter. This is 0.0002% more than 304.8 mm, the length of the international foot established by the 1959 International Yard and Pound Agreement.
The Hawks point was established by Nelson Hawks in 1879, based on a printer's foot reduced by 0.375% from the standard foot of his time. It had a value of 6996351459800000000♠0.013837 in (about 6996351460000000000♠0.35146 mm). A variant was proposed to be exactly 83 picas or 996 points in 350 mm (ca. 6999351405622000000♠0.351405622 mm/pt), giving it a value around 6996351761221800000♠0.013848867 in.
The Johnson point was established by Lawrence Johnson in the mid-1800s based on a printer's foot 249⁄250 as large as the standard foot (11.952 inches or 0.996 foot). It thus had a value of 0.01383 inch. The 15th meeting of the Type Founders Association of the United States (ATA) approved the "Johnson pica" as its official standard in 1886, hence the alias ATA point. Following the 1959 standardization of the foot, this meant the American printer's foot was 303.5808 mm exactly and its point became 351.36 µm.
This size was approximated by Donald Knuth for the default unit of his TeX computer typesetting system and is thus sometimes known as the TeX point, which is 351.45980 µm or exactly 1⁄72.27 of the modern inch, and exactly 800⁄803 of the PostScript point (bp in TeX).
Like the French Didot point, the traditional American printer's point was largely replaced by the DTP point system.
Desktop publishing point
The desktop publishing point (DTP point) or PostScript point is defined as 1⁄72 or 0.0138 of the international inch, making it equivalent to 352.7 µm. Twelve points make up a pica, and six picas make an inch. A separate typographic or printer's foot is not needed anymore.
This specification was developed by John Warnock and Charles Geschke when they created Adobe PostScript. It was adopted by Apple Computer as the standard for the display resolution of the original Macintosh desktop computer and the print resolution for the LaserWriter printer.
In 1996, it was adopted by W3C for Cascading Stylesheets (CSS) where it was later related at a fixed 4:3 ratio to the pixel due to a general (but wrong) assumption of 96 px/in screens.
Point-size names
Fonts originally consisted of a set of moveable type letterpunches purchased from a type foundry. As early as 1600, the sizes of these types—their "bodies"—acquired traditional names in English, French, German, and Dutch, usually from their principal early uses. These names were used relative to the others and their exact length would vary over time, from country to country, and from foundry to foundry. For example, "agate" and "ruby" used to be a single size "agate ruby" of about 5 points; metal type known as "agate" later ranged from 5 to 5.8 points. The sizes were gradually standardized as described above. Modern Chinese typography uses the following names in general preference to stating the number of points. In ambiguous contexts, the word hào (t 號, s 号, lit. "number") is added to the end of the size name to clarify the meaning.
Note that the Chinese font sizes use American points; the Continental systems traditionally used the Fournier or Didot points. The Fournier points, being smaller than Didot's, were associated with the names of the Didot type closest in size rather than identical in number of points.