The aspect ratio of group A paper size is √ 2: 1, and then the nearest millimeter value is rounded. A0 is defined as paper with an area of one square meter and an aspect ratio of √ 2: 1. The following paper sizes, such as A 1, A2, A3, etc. , are defined as the paper with one digit missing is folded in half along the long side and then discarded to the nearest millimeter value.
The size of group B paper is the geometric average of the same number of sheets and one less number of sheets of group A paper. Before the popularization of printers, group B paper was mostly used.
Use A4 and B5.
A4 has many uses: daily copying, printing, contracts, documents, tenders, publicity pages, writing letters, etc.
B5 paper is small in size, and is often used to make books, notebooks, paper and student paper in schools.