Envelope Sizes - C0, C1, C2, C3, C4, C5, C6, C7, C8, C9, C10 & DL Envelopes (2024)

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The dimensions of the C series envelope sizes, as defined by ISO 216, are given in the table below right in both millimetres and inches (cm measurements can be obtained by dividing the mm value by 10). The diagram below shows the size of each of the envelopes when compared to a sheet of A4 paper. are not covered by ISO 216 and are covered on this page.

To obtain sizes in centimetres, convert mm values to cm by dividing by 10 and infeet by dividing inch values by 12. More units here.

C Series Envelope Size Tolerances

Tolerances specified in ISO 216 for the C series envelope sizes are the same as for A & Bseries 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 numberi.e. C4 dimensions are the geometric mean of A4 and B4. This produces a size between the two thatmakes an envelope that will neatly hold the A series paper of the same size, thus a C4 envelopeis 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 becauseof this an A4 sheet folded parallel to its shortest sides will fit in a C5 envelope and foldedtwice will fit a C6 envelope.

The following diagrams show C4, C5 and C6 envelopes compared to A4 paper size (the envelope being shown inbrown with the paper shown as grey) as can be seen in the first diagram the C4 envelope can contain an A4sheet, the C5 envelope can contain an A4 sheet folded in half (an A5 sheet) and the C6 envelope can containan A4 sheet folded in half twice (an A6 sheet). This is the reason that you will sometimes see theseenvelope sizes being referred to as A4 envelope size, A5 envelope size and A6 envelope size.

C4 Envelope

C5 Envelope

C6 Envelope

DL Envelope Size - The Business Envelope Extension

One of the most widely used business envelopes, the DL format does not fall under the C seriessizes as it has a different aspect ratio. This envelope originated in Germany in the 1920's andwas known as DIN Lang, but DL is now more commonly expanded to 'Dimension Lengthwise'. Thissize is defined in the ISO standards for envelope sizes, as the standard would have been remissin omitting the most commonly used business envelope size.

The dimensions of DL are 110 x 220 mm (4⅓" x 8⅔") and as such the DL envelope willhold an A4 sheet of paper folded into 3 equal sections parallel to its shortest sides.

Despite complaints from manufacturers of automatic enveloping machines that it is slightly toosmall for reliable enveloping and the introduction of a C6/5 envelope at 114 x 229 mm, the originalDL size continues to be most commonly used.

DL+ and DL++

DL+, at 114 x 229 mm, is another name for the C6/C5 envelope and DL++ is slightly bigger again at 114 x 235 mm

B4 and B6 Envelope Sizes

Although initially specified as paper sizes both B4 and B6 have come to be used as envelope sizes in various countries around the world.

Note: Some sites list B4 envelopes at 352mm

Other Envelope Sizes C5+, C5++, C7/C6 and A3

These envelope sizes are available from some suppliers and we have listed them here for completeness

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