100 years of DIN A4: the most famous 29.7 by 21 centimeters

Finally, we owe the abolition of the “Groß-Patria”, “Super-Royal”, “Folio” or “Imperial” to a native of the Erzgebirge. Letters, certificates, invoices, posters or cards are usually no longer printed in paper formats that sometimes appear royal, but according to relatively sober industrial standards such as DIN A4 or DIN A3. This goes back to the engineer and mathematician Walter Porstmann.

Exactly 100 years ago, the German Institute for Standardization (DIN) published its guideline 476 for paper formats based on Porstmann’s work on Thursday (August 18). Since then, the A4 type and its siblings have been the benchmark for everything in the office and school.

Dimensions such as 29.7 x 21 centimeters for an A4 sheet may seem arbitrary. But the series is based on an almost perfect measure: the square meter. The 118.9 by 84.1 centimeters of the basic A0 format form an area of ​​0.999949 square meters. The minimal deviation is due to the side lengths being rounded to whole millimeters.

For the next smaller version, the longer side edge is halved. The numbers indicate how often the basic size A0 is folded – for example four times for A4.

The proportions of the two side lengths also follow a geometric perfection: They are related to each other like the edge to the diagonal of a square – that is, in the ratio 1 to the square root of 2 (or roughly: about 7 to 10). Porstmann (1886-1959) once wrote that this proved “very useful in all kinds of applications”. “It is the only form that, when a format is continuously halved, delivers nothing but similar partial formats.”

The engineer can thus draw on knowledge far ahead of his time. Already in 1786, the natural scientist and philosopher Georg Christoph Lichtenberg (1742-1799) from Göttingen wrote about this image format: “The form has something pleasant and excellent compared to the usual.”

Porstmann was unmistakably inspired by the philosopher and chemistry Nobel laureate Wilhelm Ostwald (1853-1932), as his private secretary and assistant he worked near Leipzig from 1912. It is sometimes said that he arbitrarily appropriated his mentor’s ideas – leading to a rift in 1914.

A basis for Ostwald’s teaching is the principle of completeness. This does not include, for example, waste of material and space. Among other things, he developed a “world format for printed matter”, which, however, did not find favor in practice because its dimensions did not fit with the formats that were common at the time.

Ostwald’s idea is based on an economic approach: by using standard dimensions for paper (PDF documents), for example, libraries can save space on their shelves by no longer having to store books of different sizes. And it has another advantage: “Due to the complexity of the paper machines and printing presses, which must be ready for all possible formats, the production of the books is much more expensive than it would be if uniform formats were used.” writes Ostwald in 1911.

The Nobel laureate made demands for his “world format” (PDF document), which was later also fulfilled in the DIN A series: it must be possible to produce different sizes simply by folding, and the resulting rectangles (in the ratio of 1 to the square root of ​​2) must be similar to each other. The difference between DIN and the “world format” is that the square meter is defined as the starting measure – and not, as with Ostwald, a specific side length in centimeters.

With his book “Normenlehre” from 1917, Porstmann drew the attention of the top floor of the Standard Committee of German Industry (now the German Institute for Standardization, DIN). After his thesis on the standardization of measurement systems, he worked from 1920 in a leading position at the institute.

After the publication of the 476 directive, dimensions take over the world. The first institutional user is the Reichsbahn head office. In Germany, paper for commercial and public purposes will soon be produced exclusively according to DIN. Formats for newspapers or books, for envelopes, binders or folders are also standardized. In addition, office furniture will be adapted to the new dimensions.

Today, the DIN formats have been adapted almost everywhere in the world via the international standard ISO 216. The United States and Canada maintain independent formats. In the US, for example, the “Letter” format with dimensions of 8.5 x 11 inches (21.59 x 27.94 centimeters) is the most common – slightly shorter and wider than A4.


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