25 open: 168mmX228mm
Folio refers to the size of a book, that is, how many pages are cut from a full-open printing paper.
For the main text of a book, the opening number has the same meaning as the folio, but for the opening number of its cover and insert sheet, its meaning is different because of its area. Usually the size of a single-page publication is called an opening, such as newspapers, wall charts, etc. are divided into full-sheet, folio, 4- and 8-sheet. Because there are several different series of international and domestic paper formats, although they are all cut into the same number, their sizes are different. Although they are collectively referred to as how many folio after binding, the sizes of the books are different.
In actual production, a full sheet with a width of 787 x 1092 mm (31 x 43 inches) is usually referred to as a positive paper; a full sheet with a size of 889 x 1194 mm (35 x 47 inches) is called a large paper Degree paper. As the format of 787 × 1092 mm paper is defined by our country and is inconsistent with international standards, it is a non-standard format that needs to be phased out. Due to many reasons such as domestic papermaking equipment, paper, and existing paper types, there is still a transition period between the old and new standards. As of 2013, the cutting specifications are largely: large 16 format 210 × 297 (mm), large 32 format 148 × 210 (mm) and large 64 format 105 × 148 (mm); the positiveness is: 16 format 188 × 265 (mm), 32 format 130 × 184 (mm), 64 format 92 × 126 (mm).