History of the A4 paper size
The idea behind A4 dates from 1786, when the Göttingen physicist Georg Christoph Lichtenberg described a sheet with an aspect ratio of 1 to √2. It only became a standard on 18 August 1922, when Walter Porstmann published DIN 476 in Germany. Since 1975 the system has been ISO 216 and is used almost everywhere.
Contents of this page
1786: Lichtenberg’s letter
On 25 October 1786, Georg Christoph Lichtenberg wrote a letter to his colleague Johann Beckmann. In it he described a sheet of paper whose half has the same shape as the whole. The short side, he wrote, should relate to the long one “as 1 : √2, or as the side of a square to its diagonal”.
Lichtenberg saw this as a pleasing mathematical curiosity, not as a proposal for a standard. He did notice, though, that a sheet in this ratio always looks the same however often it is folded. That is exactly the core of every ISO size today.
1798: the French stamp law
A few years later, revolutionary France took up the idea. A law on stamped paper from 1798 set paper sizes with a ratio of 1 to √2. One of them, the “Grand registre”, measured 420 × 594 mm, which is precisely today’s A2. The system did not catch on at the time and was forgotten again.
1910: Ostwald’s world format
Around 1910, the chemist and Nobel laureate Wilhelm Ostwald proposed a “world format”. He too used the ratio 1 to √2, but started from a side length of 1 cm and doubled from there. Ostwald thought big: books, journals and index cards were to share the same sizes worldwide so they would fit the same shelves. A few publishers did print in the world format, but it never took hold.
1922: Porstmann and DIN 476
Walter Porstmann (1886 to 1959) was an engineer and for a time Ostwald’s assistant. For the German industrial standards committee, he developed a system that made Ostwald’s idea practical. The key difference was that Porstmann did not start from a side length but from an area. The base sheet A0 was to measure exactly one square metre. That way, the weight of any sheet could be read straight from the grammage.
On 18 August 1922, the standard appeared as DIN 476 with four series: A as the main series for paper and printed matter, plus B, C and D as supplementary series for envelopes, folders and covers. German government offices switched to the new sizes over the following years, and business followed, because paper mills, printers and office furniture makers could all work to the same dimensions.
A footnote on Porstmann: he also campaigned for writing German entirely in lower case and wrote some of his own texts that way. He was rather less successful with that than with paper.
From Germany to the world
Over the following decades, more and more countries adopted the system. The UK introduced A sizes in 1959, and in 1975 they became international as ISO 216. By 1977, 88 out of 148 countries had adopted A4 as their standard letter size. Today it is used practically everywhere, with two big exceptions: the USA and Canada, which kept Letter and Legal.
The D series disappeared from the standards over time. The C series was standardised internationally as ISO 269 and withdrawn again in 2009. The current edition of ISO 216 dates from 2007.
Key dates
| Year | Event |
|---|---|
| 1786 | Lichtenberg describes the 1 : √2 ratio in a letter to Johann Beckmann |
| 1798 | French stamp law with sizes in the 1 : √2 ratio |
| around 1910 | Wilhelm Ostwald proposes the world format |
| 1922 | DIN 476 is published on 18 August |
| 1959 | the British Standards Institution adopts the A sizes |
| 1975 | ISO 216 makes the A and B series international |
| 1977 | 88 out of 148 countries use A4 as their letter size |
| 2007 | current edition of ISO 216 |
| 2009 | ISO 269 (C series) is withdrawn |
Frequently asked questions
Who invented A4?
Walter Porstmann developed the system of DIN sizes, published in 1922 as DIN 476. The idea of the aspect ratio came from Georg Christoph Lichtenberg in 1786.
When was A4 introduced?
On 18 August 1922, when DIN 476 was published in Germany.
When did A4 become an international standard?
In 1975, as ISO 216.
Why does A0 measure one square metre?
Porstmann chose area as the starting point. That makes the grammage equal to the weight of an A0 sheet, and every size easy to calculate.