A4 the size of paper is 210mm × 297mm。 A4 paper is defined by ISO 216 of the international organization for standardization. The paper size used in most countries in the world adopts this international standard.

This standard was originally incorporated into DIN by the Weimar Republic in 1922. Although some formats were developed by France at the same time, they were forgotten later.

Extended data:

1. Paper size refers to the size range of paper that can be supported by folding machine and matching machine, generally including a maximum size and a minimum size, which is generally expressed by the specification of paper. If the paper is larger or smaller than this size range, the product cannot fold and match it.

2. Group B paper size is the geometric average of group a paper with the same number and one less number. For example, B1 is the geometric average of A1 and A0. Similarly, group C paper size is the geometric average of group A and B paper with the same number. For example, C2 is the geometric average of B2 and A2. In addition, Japan has an incompatible group B paper size, which is defined by arithmetic average rather than geometric average.

3. Group C paper size is mainly used for envelopes. A piece of A4 size paper can fit into a C4 size envelope. If you fold A4 paper in half into A5 paper, it can fit into a C5 sized envelope.