The area of C series sheets is the geometric mean of the areas of the A and B series sheets of the same number; for instance, the area of a C4 sheet is the geometric mean of the areas of an A4 sheet and a B4 sheet. This means that C4 is slightly …
For example, a C4 is the geometric mean of the areas of an A4 and a B4 paper. A C4 is slightly larger than an A4 and slightly smaller than a B4. An A4 paper fits in a C4 envelope and an A4 and C4 fit in a B4 envelope.