what does the A stand for on an A4

Answer

Dear Harm,

The A4 format is part of the A series of the ISO-216 standard. That standard is in turn based on a German DIN standard (sometimes still referred to as DIN-A4).

The basic format of the A series is the A0.
The ratio between height and width for the A series is 1 to 1.4142 (= square root of 2).
The special thing about this ratio is that if you halve a leaf by halving the longest side, the new size has the same ratio again (1 to 1.4142).
An A0 has an area of ​​exactly 1m². For example, an A1 is 1/2 m², an A2 = 1/4 m², and so on. An A4 is then a 1/16 m².

The A series is used as a paper standard worldwide, with the exception of North America and some other countries.

There is also a B series (mainly used for posters) and a C series (mainly for envelopes).

Sincerely,
Roeland Pypea