What are the standards for A4 and B5 paper sizes?

A4 specification: 21*29.7 cm B4 specification: 25*35.4, B5 specification: 18.2*25.7
The specification of the paper refers to the size of the paper after being trimmed and cut to a certain extent. In the past, how much "paper size" (for example, 8-open or 16-open) was used to indicate the size of paper. Now I use international standards, rules are as follows: A0, A1, A2, B1, B2 ...... to indicate the width of the paper. The ratio of the width (in X) and length (in Y) of the paper is X: y = 1: N.
According to the basic area of the paper width, the width is divided into Series A, Series B, and Series C. The width of the width is 841mm × 1189mm and the width is 1 m² mm; the size of the B0 format is 1000mm × 1414mm, the size of the format is 2.5 m² mm × 917mm, and the size of the C0 format is 1279mm × 2.25 m² mm; the format of the paper only uses Series A and Series B. If the A0 paper is split into two equal points along the length, it becomes the A1 specification, and the A1 paper is split along the length direction to become the A2 specification, so it is split to the A8 specification; b8 paper is also split to the B8 specification according to this method. A0 ~ A8 and B0 ~ The size of B8 is listed in the following table. Among them, A3, A4, A5, A6, B4, B5, B6, and other seven kinds of format specifications are commonly used for copying paper.
For example, "A4" paper is to fold a-type basic paper four times. Therefore, the area of an A4 paper is one of the 4 power points of 2 of the basic area, that is, 1/16. The rest.
Generally, the printing paper adopts the copy paper, which is classified by size. There are several standards: 1. A; 2. B; 3. K, k-paper is what we often say about it. K-paper is only available in China. A-type paper is generally used. Regardless of type A, its classification is like this. For example, A5 is twice that of A6, A4 is twice that of A5, and A3 is twice that of A4, b4 is twice that of B5 B3 is twice that of B4, while K-type classification divides a large 1 K paper into two sheets of 2 K, divide 2 k paper into 4 K in half, divide 4 K into 8 K in half, divide 8 K into 16 K in half, and divide 16 k into 32 K in half.
There is also dedicated office printing paper, which is classified by the size and layers of paper, such as 241-1,241-2. They represent Layer 1 and Layer 2 narrow Row printing paper, respectively, of course there are 3 layers and 4 layers; commonly used Wide Row printing paper also has 381-1,381-2 and so on.
There are also parts based on the thickness of the paper, such as 60g, 70g, 75g, 85g, 120g, etc., refers to the weight of the paper per unit area is multiple, because the paper density is basically the same, the heavier the weight of the paper per unit area, the thicker the paper thickness. For example, the printer generally uses about 40 GB of paper, while the all-in-one machine uses 50-60 GB of paper, and the copier uses 70-GB of paper, generally, do not use paper below 60g thick for printers; otherwise, it is easy to jam.