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C Series Envelopes – C envelope size chart C0, C1, C2, C3, C4, C5, C6, C7, C8

C series envelope size chart Click the above C series envelope chart to view a larger version.

Popular Envelope Sizes and Printing Formats with C Series Envelopes

The C series is used only for envelopes and is defined in ISO 269. 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 larger than A4, and B4 slightly larger than C4. The practical usage of this is that a letter written on A4 paper fits inside a C4 envelope, and a C4 envelope fits inside a B4 envelope.

The C series formats are geometric means between the B series and A series formats with the same number, (e.g., C2 is the geometric mean between B2 and A2). The C series formats are used mainly for envelopes. An A4 page will fit into a C4 envelope. C series envelopes follow the same ratio principle as the A series pages. For example, if an A4 page is folded in half so that it is A5 in size, it will fit into a C5 envelope (which will be the same size as a C4 envelope folded in half).

A, B, and C paper fit together as part of a geometric progression, with ratio of successive side lengths of 21/8, though there is no size half-way between Bn and An-1: A4, C4, B4, “D4″, A3, …; there is such a D-series in the Swedish extensions to the system.

The exact millimetre measurement of the long side of Cn is given by 1000/(2(4n-3)/8)+0.2.

ISO C envelope sizes in millimetres and in inches

Format C series
Size mm × mm in × in (inches)
C0 917 × 1297 36.1 × 51.1
C1 648 × 917 25.5 × 36.1
C2 458 × 648 18.0 × 25.5
C3 324 × 458 12.8 × 18.0
C4 229 × 324 9.0 × 12.8
C5 162 × 229 6.4 × 9.0
C6 114 × 162 4.5 × 6.4
C7 81 × 114 3.2 × 4.5
C8 57 × 81 2.2 × 3.2
C9 40 × 57 1.6 × 2.2
C10 28 × 40 1.1 × 1.6
View paper sizes and chart of (A) Series Paper »
View paper sizes and chart of (B) Series Paper »