C2

The C2 paper size has dimensions of 458 x 648 mm, making it the third largest size in the C series of envelopes defined in ISO 269 (withdrawn in 2009). With a surface area of 0.28 m2, C2 is a less commonly used oversized envelope format. As part of the C series based on geometric means between A and B series sheets, C2 falls between A2 (420 x 594 mm) and B2 (500 x 707 mm). While not typical, C2 envelopes can occasionally be useful for mailing large folded documents, posters, and other items requiring an oversized envelope. The C series origins trace back to early 20th century efforts in Germany to define paper sizes based on geometric principles, later included in ISO standards.