C7

The C7 paper size has dimensions of 81 x 114 mm, making it the eighth largest size in the C series of envelopes defined in ISO 269 (withdrawn in 2009). With a surface area of 0.009 m2, C7 is a moderately used envelope size. As part of the C series based on geometric means between A and B series sheets, C7 falls between A7 (74 x 105 mm) and B7 (88 x 125 mm). Key uses of C7 envelopes include mailing small documents, compact discs, invitation cards, and other flat items needing more space than a standard business or note envelope. The origins of C7 and other C sizes trace back to early 20th century German efforts to define paper sizes based on geometric principles, later incorporated into ISO standards.