This is a very common specification. A5 paper, that is, A-type paper with basic size, is folded five times, so the area of an A5 paper is one-fifth of the area of the basic paper, that is, 1/32. A5 paper is half of A4 paper, commonly known as No.32 paper.

Other common paper types: A3 (A3(8K)420mm×297mm；; a4( 16k)297mm×2 10mm； A6 (64k) 144mm× 105mm。

China has adopted international standards, and stipulated that A0, A 1, A2, B 1, B2 ... should use other marks to express paper format specifications. According to the standard, the proportional relationship between the width (represented by X) and the length (represented by Y) of paper is X: Y =1:N. ..