Envelope Size Guide

 Size Unit Height x Width C0   C1   C2   C3   C4   C5   C6   C7   C8   C9   C10   US in mm   inches is

How do you know what size envelope is right for your piece of paper?

The following diagrams illustrate some common standard envelope sizes in comparison with the size of a sheet of A4 paper.

This is a C4 size envelope (324x229mm), one of the most common envelopes. It can hold a sheet of unfolded A4 paper.

This is a C5 size envelope (229x162mm) compared to A4 paper. It can hold a piece of A4 paper folded in half once or a piece of unfolded A5.

This is a C6 size envelope (114x162mm) compared to A4 paper. It can hold a piece of A4 paper folded into quarters, an A5 piece of paper folded in half once or a piece of unfolded A6.

This is a DL size envelope (110x220mm) compared to A4 paper. It can hold a A4 piece of paper folded into thirds or an A5 piece of paper folded once, this style of envelope is most commonly used in buisness.

C-Series Envelopes

A certain set of envelope sizes in common use are called the C-series and designated C4, C3, etc. These are defined from ISO 216 and are the geometrical mean of the A and B size envelopes, therefore C4 is bigger than A4, but smaller than B4. (More infomation can be found about A & B paper sizes here)

The table below shows the size of C-series envelopes, along with the dimensions of them in both millimetres and inches and compares them to the A paper size that they will hold unfolded:

Format Dimensions (mm) Dimensions (in) Holds A Size
C10 28 x 40 1.1 x 1.6 A10
C9 40 x 57 1.6 x 2.2 A9
C8 57 x 81 2.2 x 3.2 A8
C7 81 x 114 3.2 x 4.5 A7
C7/C6 81 x 162 3.2 x 6.4 A7
C6 114 x 162 4.5 x 6.4 A6
C6/C5 114 x 229 4.5 x 9.0 A6
C5 162 x 229 6.4 x 9.0 A5
C4 229 x 324 9.0 x 12.8 A4
C3 324 x 458 12.8 x 18.0 A3
C2 458 x 648 18.0 x 25.5 A2
C1 648 x 917 25.5 x 36.1 A1
C0 917 x 1297 36.1 x 51.5 A0

Note: Centimetres (cm) values can be obtained by dividing millimetres by 10 and metres (m) by dividing millimetres by 100. Dimensions in feet can be obtained by dividing inches by 12.

The C6/C5 envelope size was introduced as a replacement for the DL envelope (mainly to allow a little more tolerance for automatic enveloping machines), however it has never really caught on and most DL style envelopes still measure 110x220 mm.

DL+ and DL++ Envelope Sizes

DL+ is used as an alternative name for the C6/C5 envelope 114mm x 229mm. DL++ is, as you might expect, slightly larger again at 114mm x 235mm.

Format Dimensions (mm) Dimensions (in)
DL 110 x 220 4.3 x 8.7
DL+ 114 x 229 4.5 x 9.0
DL++ 114 x 235 4.5 x 9.3

B4 and B6 Envelopes

Although specifed as paper sizes by ISO, B4 and B6 have also come into use as envelope sizes.

Format Dimensions (mm) Dimensions (in)
B4 250 x 353 9.8 x 13.9
B6 125 x 176 4.9 x 6.9