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International Envelope Series



Belonging to the ISO 216 series, the C4 paper size is a significant player in the international standard for paper sizes. This particular size measures 229 x 324 millimeters or approximately 9.0 x 12.8 inches, making it an ideal choice for various professional and personal applications.

The C4 paper size is part of the 'C' series in the ISO standard, designed specifically to serve as envelopes for the 'A' series. In this context, a C4 envelope can comfortably accommodate an unfolded A4 sheet, which is one of its most common uses worldwide.

C4 paper dimensions


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2A046.81 x 66.221189 x 1682119 x 1683370 x 4768
A120.51 x 0.7113 x 181 x 237 x 51
4A066.22 x 93.621682 x 2378168 x 2384768 x 6741
A110.71 x 1.0218 x 262 x 351 x 74
A101.02 x 1.4626 x 373 x 474 x 105
A3+12.95 x 19.02329 x 48333 x 48933 x 1369
A1+23.98 x 35.98609 x 91461 x 911726 x 2591
A0+35.98 x 50.87914 x 129291 x 1292591 x 3662
A64.13 x 5.83105 x 14811 x 15298 x 420
A55.83 x 8.27148 x 21015 x 21420 x 595
A48.27 x 11.69210 x 29721 x 30595 x 842
A311.69 x 16.54297 x 42030 x 42842 x 1191
A91.46 x 2.0537 x 524 x 5105 x 147
A216.54 x 23.39420 x 59442 x 591191 x 1684
A82.05 x 2.9152 x 745 x 7147 x 210
A123.39 x 33.11594 x 84159 x 841684 x 2384
A72.91 x 4.1374 x 1057 x 11210 x 298
A033.11 x 46.81841 x 118984 x 1192384 x 3370

Interestingly, this specific sizing system was first introduced by Germany in 1922 before being adopted internationally. The logic behind its design lies in its aspect ratio - when you cut or fold any C-series page in half along its longest side, it will retain its original aspect ratio.

Moreover, while ANSI standards are more prevalent within North America's borders, ISO standards like C4 are widely recognized and used globally due to their practicality and consistency across different formats.

In conclusion, whether you're sending out professional correspondence or storing important documents safely without folding them multiple times over - consider using a C4 envelope. Its dimensions make it versatile enough to handle various tasks while maintaining a consistent aspect ratio that ensures your documents always fit perfectly.

Other Formats in the International Envelope Series

Interesting facts about C4

1: C4 Paper Size

C4 paper is part of the ISO 216 standard series and measures 229 x 324 millimeters (9.02 x 12.76 inches). It is commonly used for envelopes and fits an unfolded A4 sheet perfectly.

2: Envelope Compatibility

The name "C4" comes from its compatibility with the C series envelope sizes. When a C4 paper is folded in half, it fits perfectly into a C5 envelope, which can then fit into a larger C6 envelope.

3: International Standardization

The ISO 216 standard for paper sizes, including C4, was first introduced in Germany in the early 20th century. It aimed to establish a consistent system for paper dimensions worldwide.

4: Historical Connection

The ISO A-series and B-series paper sizes were developed based on the geometric mean of their respective dimensions. However, the C-series (including C4) was derived by dividing an A-series sheet into two equal parts.

5: Common Usage

Certain countries, such as Germany and Austria, use the DIN standard instead of ISO when referring to paper sizes. In this system, C formats are often preferred for business correspondence due to their convenient proportions.

6: Envelope Window Placement

In some countries like France and Belgium, envelopes designed for business correspondence often have a window cutout on the left-hand side to display recipient addresses conveniently when using unfolded A-size sheets like A3 or A2 inside a corresponding-sized envelope like C3 or C2 respectively.


Certain facts about C4 paper may vary depending on regional standards and practices. It is always advisable to consult the specific guidelines and requirements of your country or organization when dealing with paper sizes.