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International Envelope Series



Belonging to the ISO 216 standard, the C9 paper size is a unique and often overlooked member of the C series. This particular size measures 40 x 57 millimeters, making it one of the smallest in its series. Its compact dimensions make it an ideal choice for specific applications where space is at a premium.

As part of the ISO's international standard, C9 shares a common aspect ratio with other sizes in its series. This ratio, √2:1, ensures that when two same-sized C9 sheets are placed side by side or atop one another, they form the next size up in the series - in this case, a C8 sheet.

C9 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

The intriguing fact about this paper size is that it's primarily used for envelopes designed to accommodate B10 sheets. The slightly larger dimensions of a C9 envelope compared to a B10 sheet allow for easy insertion and removal while providing adequate protection during transit.

In comparison with ANSI standards prevalent in North America, there isn't an exact equivalent for C9. However, its closest counterpart would be considered 'Check' sized at 3.5 x 8.5 inches.

Despite its diminutive stature within the grand scheme of paper sizes, don't underestimate the potential impact of utilizing C9 effectively. Whether you're crafting personalized direct mail campaigns or creating unique event invitations, this small but mighty paper size can deliver big results when used strategically.

Other Formats in the International Envelope Series

Interesting facts about C9

1: C9 paper is part of the ISO 216 standard

C9 paper is a specific size within the ISO 216 standard, which defines international paper sizes. It is commonly used for envelopes and measures approximately 162 mm x 229 mm.

2: C9 paper is also known as an envelope size

The C9 designation refers to a specific envelope size that can accommodate A9-sized documents. It provides a standardized option for mailing or storing documents of that size.

3: C9 envelopes are often used for formal invitations

Due to their larger size, C9 envelopes are frequently chosen for formal invitations, such as wedding invitations or corporate event announcements. The extra space allows for elegant designs and additional inserts.

4: The aspect ratio of C9 paper is approximately √2

The aspect ratio of C9 paper (width divided by height) is approximately equal to the square root of two (√2). This ratio remains consistent across all ISO paper sizes and ensures easy scaling between them.

5: The dimensions of C9 paper have historical origins

The dimensions of C9 (162 mm x 229 mm) can be traced back to traditional British foolscap folio sheets, which were widely used in the past. These sheets were later standardized into the ISO system, with slight modifications.

6: The use of C series envelopes simplifies document handling

C series envelopes, including C9, provide a convenient way to handle documents without folding or creasing them. They allow important papers to be stored or mailed in their original unfolded state.

7: C9 paper is compatible with A9-sized documents

C9 envelopes are designed to perfectly fit A9-sized documents, which measure approximately 148 mm x 210 mm. This compatibility ensures that the contents of the envelope remain secure and undamaged during transit.

8: C9 envelopes can be made from various types of paper

C9 envelopes can be manufactured using different types of paper, including standard bond paper, recycled paper, or specialty papers like vellum or parchment. The choice of material depends on the desired appearance and purpose.

9: C series envelopes have a long history

The use of standardized envelope sizes, including C series envelopes like C9, dates back to the early 20th century. The ISO 216 standard was established in the 1970s to further streamline international paper sizes and envelope dimensions.

10: C9 is just one size in a comprehensive range

The ISO 216 standard includes a wide range of sizes beyond C9. From smaller A-series sheets to larger B-series sheets and various envelope sizes (C-series), there are options available for almost every document need.