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

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 |