This is more than ten years old talk from one of my favourite YouTube channels Gresham College by professor John D. Barrow (1952-2020).
It talks about the different paper sizes we have and what are their mathematical properties.
Here are some screenshots with interesting information.
International standard paper sizes.
A series
Georg Christoph Lichtenberg proposed the standardized paper size system used globally today except in Canada and the US defined by ISO 216, which has A4 as the most commonly used size.
B series
C series
Uses
American Paper Sizes
Golden Ratio
Medieval books
Tauno Erik 