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. 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, 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 ). In 1878,
Hermann Berthold defined 798 points as being equal to 30 cm, or 2660 points equalling 1 meter: that gives around to the point. A more precise number, , sometimes is given; This size is still mentioned in the technical regulations of the
Eurasian Economic Union.
Metric points pdfTEX, but not plain TeX or LaTeX, also supports a
new Didot point (
nd) at mm or and refers to a not-further-specified 1978 redefinition for it. The
French National Print Office adopted a point of mm or in about 1810 and continues to use this measurement today (though "recalibrated" to ). Japanese and German
American points The basic unit of measurements in American typography was the pica, usually approximated as one sixth of an inch, but the exact size was not standardized, and various type foundries had been using their own. While living there he had close contact with the Fournier family, including the father and
Pierre Simon Fournier. Franklin wanted to teach his grandson
Benjamin Franklin Bache about printing and typefounding, and arranged for him to be trained by Francois Ambroise Didot. Franklin then imported French typefounding equipment to Philadelphia to help Bache set up a type-foundry. Around 1790, Bache published a specimen sheet with some Fournier types. After the death of Franklin, the matrices and the Fournier mould were acquired by Binny and Ronaldson, the first permanent type-foundry in America. Successive mergers and acquisitions in 1833, 1860 and 1897 saw the company eventually become known as MacKellar, Smith & Jordan. The Fournier cicero mould was used by them to cast pica-sized type.
Nelson Hawks proposed, like Fournier, to divide one American inch exactly into six picas, and one pica into 12 points. However, this saw an opposition because the majority of foundries had been using picas less than one sixth of an inch. So in 1886, after some examination of various picas, the Type Founders Association of the United States approved the pica of the
L. Johnson & Co. foundry of Philadelphia (the "
Johnson pica") as the most established. The official definition of one pica is , and one point is . That means 6 picas or 72 points constitute standard inches. A less precise definition is one pica equals , and one point . It was also noticed that 83 picas is nearly equal to 35 cm, so the Type Founders Association also suggested using a 35 cm metal rod for measurements, but this was not accepted by every foundry. This is sometimes known as the . Since 1 inch is exactly 25.4 mm, it follows that, 1 TeX pt = in = 0. in = 0. mm. This is trivially different from the American point.
Old English points Although the English Monotype manuals used 1 pica = , their manuals used on the European continent use another definition. There, 1 pica = , the Old English pica. As a consequence all the tables of measurements in the German, Dutch, French, Polish and all other manuals elsewhere on the European continent for the composition caster and the super-caster are different in quite some details. The Monotype wedges used at the European continent are marked with an extra 'E' behind the set-size: for instance: 5-12E, 1331-15E etc. When working with the E-wedges in the larger sizes, the differences will increase even more.
Desktop publishing point The
desktop publishing point (DTP point) or
PostScript point is defined as or 0.013 of an inch, making it equivalent to mm = 0.352 mm. Twelve points make up a pica, and six picas make an inch. The PS documentation only calls this length "unit size" and notes: This specification was found in the Xerox Interpress language used for its early digital printers and further 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 Style Sheets (CSS) where it was later related at a
fixed 3:4 ratio to the
pixel (e.g. 12 pt and 16 px are the same in CSS) due to a general (but wrong) assumption of 96
pixel-per-inch screens.
Resolution-dependent point Since the advent of high-density
"Retina" screens with a much higher resolution than the original 72 dots per inch, Apple's programming environment
Xcode sizes
GUI elements in
points that are scaled automatically to a whole number of physical
pixels in order to accommodate for screen size, pixel density and typical viewing distance. This
Cocoa point is equivalent to the
pixel px unit in
CSS, the
density-independent pixel dp on
Android and the
effective pixel epx or ep in Windows
UWP. == Font sizes ==