C7

The C7 envelope is one of the smallest ISO standard envelope sizes, with compact dimensions of 114mm x 81mm giving it a surface area of 9,234 mm2. The maximum enclosure size is approximately 76mm x 108mm. As part of the ISO 216 series, the C7 gets its designation from being able to accommodate an A5 sheet of paper folded into thirds widthwise. An A5 sheet measures 148mm x 210mm and folds to 81mm x 210mm, fitting neatly into a C7 envelope. This makes the C7 well-suited for sending compact letters, postcards, greeting cards, and invitations originating from A5 paper. However, its small size limits what it can carry. The C7 is not as widely used as slightly larger sizes like C6 or C5 but serves a niche for very small mailings. It provides only a bit more space than a large postcard. The abbreviated C7 name is sometimes written as C7/6 to indicate it's between C6 and C8 sizes.