ISO 216 specifies
international standard (ISO)
paper sizes used in most countries in the world today. It is the standard which defines the commonly available A4 paper size. The underlying principle is that when folded in half length-wise the paper retains its original aspect ratio
.
The international ISO standard is based on the German DIN standard 476 (DIN 476) from 1922.
The formats that became A2, A3, B3, B4 and B5 were developed in France, and published in 1798 during the French Revolution, but were subsequently forgotten.[1]
The aspect ratio used by this standard was mentioned in a letter by the German Georg Christoph Lichtenberg, written on 25 October 1786.[2]
