The dimensions of the C series envelope sizes, as defined by ISO 216, are given in the table below in both millimetres and inches (cm measurements can be obtained by dividing the mm value by 10). The diagrams to the right show the size of each of the envelopes when compared to a sheet of A4 paper.
TABLE OF ENVELOPE SIZES FROM C0 TO C10
C SERIES PAPER SIZE TOLERANCE:
Tolerances specified in ISO 216 for the C series envelope sizes are the same as for A & B series paper sizes and are as follows:
- ±1.5 mm (0.06 in) for dimensions up to 150 mm (5.9 in)
- ±2 mm (0.08 in) for lengths in the range 150 to 600 mm (5.9 to 23.6 in)
- ±3 mm (0.12 in) for any dimension above 600 mm (23.6 in)
C SERIES ENVELOPE SIZE DEFINITIONS:
C envelopes sizes are defined as the geometric mean of the A and B sizes with the same number i.e. C4 dimensions are the geometric mean of A4 and B4. This produces a size between the two that makes an envelope that will neatly hold the A series paper of the same size, thus a C4 envelope is perfect for an A4 sheet of paper unfolded.
It should be noted that C format envelopes also have an aspect ratio of 1:root2 and because of this an A4 sheet folded parallel to its shortest sides will fit in a C5 envelope and folded twice will fit a C6 envelope.