who came up with a4 paper!!!

The A4 paper size is part of the ISO 216 standard, which was based on a system originally conceived by

Dr. Walter Porstmann in Germany in the early 20th century. Porstmann developed the concept of using a paper size with an aspect ratio of 2\sqrt{2}2​, which allows for consistent scaling of documents.

Key Developments in the History of A4 Paper:

• Early Concepts (1786): The idea of a paper size system with a 2\sqrt{2}2​ aspect ratio was first proposed by
• Georg Christoph Lichtenberg, a German scientist and philosopher.
• He recognized that this ratio would allow for easy scaling between sizes while maintaining the same proportions.
• Walter Porstmann’s Contribution (1922): Building on Lichtenberg’s ideas, Walter Porstmann formalized the A-series paper sizes, including A4, as part of the German standard DIN 476 in 1922. This system organized paper sizes in a logical and scalable way, making it easier to manage and reproduce documents.
• Adoption of ISO 216 (1975): The A-series, including A4, was internationally standardized in 1975 with the adoption of ISO 216. This made A4 the most commonly used paper size in countries worldwide, except for those like the United States and Canada, which use different standards (e.g., Letter size).

The 2\sqrt{2}2​ aspect ratio was a key innovation that facilitated the widespread use of A4 paper, allowing it to be conveniently scaled up or down (e.g., from A4 to A3 or A5) while maintaining the same proportions. This consistency has made A4 an efficient and versatile choice for documents globally.

1. The Concept of the 2\sqrt{2}2​ Aspect Ratio

• Georg Christoph Lichtenberg (1786): The earliest known mention of the 2\sqrt{2}
  2 aspect ratio for paper sizes came from German scientist Georg Christoph Lichtenberg. 
• He suggested that this ratio would allow for consistent scaling by simply halving or doubling the paper’s size without altering its proportions. 
• This means that if you fold an A4 sheet in half, you get an A5 sheet with the same aspect ratio.

2. Walter Porstmann and DIN 476 (1922)

• Walter Porstmann: A German engineer and scientist, Walter Porstmann, expanded on Lichtenberg’s ideas to develop a practical system of paper sizes. 
• In 1922, he introduced the DIN 476 standard, which formalized the A-series paper sizes, including A4.