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Standard Envelope Sizes

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The dimensions found on this page are that of the ISO 269 standard dimensions. The dimensions of the envelopes found on this page compliment ISO 216 standard paper dimensions such as A4, A5, etc.

There is no ISO standard size for windowed envelopes. However, DIN 680(German Institute for Standardisation) has standard dimensions of where the window should sit, and how high and wide it should be in correspondence to the dimensions. Learn more about Window Envelopes and the standards that suit them.

Standard Envelope Size

Looking for US Standard Sizes?

DL Envelope Size


DL envelopes are otherwise known as Dimension Lengthwise envelopes. They are commonly used by businesses for formal letters. An A4 sheet folds twice length-ways to fit inside an DL envelope, where an A5 piece of paper folds once width-ways to fit inside. Due to how difficult DL size is to manufacture, a new standard called the DIN 678 standard came into being. This new standard size is known as the C6/C5 envelope.

Millimetres (mm)Centimetres (cm)Inches (In)
W x H220 x 11022 x 118.66 x 4.33

C0 Envelope Size


The C0 envelope size is the largest standard size, allowing this envelope to easily fit an A0 sheet inside of it. The Dimensions of A0 are used as a standard for all ISO 216 paper sizes, and therefore C series sizes too.

Millimetres (mm)Centimetres (cm)Inches (In)
W x H917 x 129791.7 x 129.736.1 x 51.5

C1 Envelope Size


The C1 envelope was designed with the A1 paper size standard in mind. A folded A0 piece of paper could fit inside width-ways. This size is great for holding art work.

Millimetres (mm)Centimetres (cm)Inches (In)
W x H648 x 91764.8 x 91.725.5 x 36.1

C2 Envelope Size


The C2 standard envelope size is made for A2 page, or A1 page folded width-ways. This size is commonly used for architectural drawings, posting large calenders and keep posters unfolded.

Millimetres (mm)Centimetres (cm)Inches (In)
W x H458 x 64845.8 x 64.818 x 25.5

C3 Envelope Size


The dimensions of C3 envelopes allow ISO 216 standard A3 size sheets, or A2 folded width-ways down the centre. C3 size is perfect for CAD drawings, diagrams and information that cannot be folded into a C4 envelope.

Millimetres (mm)Centimetres (cm)Inches (In)
W x H324 x 45832.4 x 45.812.8 x 18

C4 Envelope Size


C4 size is one of the most popular on this list, mainly because it houses A4 page size, or A3 folded width-ways through the centre. Official documents that shouldn't be folded are usually mailed with an C4 envelope. It's common practice to send booklets, magazines and other heavy objects in the C4 size, but the envelope is usually of the padded variety for extra strength.

Millimetres (mm)Centimetres (cm)Inches (In)
W x H229 x 32422.9 x 32.49 x 12.8

C5 Envelope Size


The standard size of C5 envelopes are most common with greeting and birthday cards, allowing A5 paper or cards to fit in snuggly. An A4 sheet can fit in if folded.

Millimetres (mm)Centimetres (cm)Inches (In)
W x H162 x 22916.2 x 22.96.4 x 9

C6/C5 Envelope Size


The C6/C5 envelope standard dimensions were added after the C series was introduced, hence the name. It was established because DL size was hard to manufacture, and therefore slightly more expensive for customers. C6/C5 fits A4 inside is folded in thirds length-ways.

Millimetres (mm)Centimetres (cm)Inches (In)
W x H229 x 11422.9 x 11.49.0 x 4.5

C6 Envelope Size


While small, C6 is one of the most popular standards for greeting cards such as Christmas cards. It allows an A6 piece of paper inside without folding, or an A5 if folded width-ways.

Millimetres (mm)Centimetres (cm)Inches (In)
W x H114 x 16211.4 x 16.24.5 x 6.4

C7/C6 Envelope Size


C7/C6 was introduced with C6/C5 size. Its purpose is to house A5 paper in the same way that C6/C5 and DL house A4 paper. So an A5 sheet folded into thirds length-ways.

Millimetres (mm)Centimetres (cm)Inches (In)
W x H162 x 8116.2 x 8.16.4 x 3.2

C7 Envelope Size


C7 envelopes house A7 paper, which is used for wedding invitations and other forms of invitation.

Millimetres (mm)Centimetres (cm)Inches (In)
W x H81 x 1148.1 x 11.43.2 x 4.5

C8 Envelope Size


C8 is so small that it can fit in the palm of your hand. Even so, it's used to mail driver's licenses, bank cards and business cards.

Millimetres (mm)Centimetres (cm)Inches (In)
W x H57 x 815.7 x 8.12.2 x 3.2

Other Sizes

The C9 and C10 dimensions are so small that it's fairly uncommon practice to use them. B6, B5, B4 and E4 are all used to place C and B envelopes inside envelopes. So B6 fits C6, B5 fits C5 and B4 fits C4. E4 on the other hand fits B4.

W x HMillimetres (mm)Centimetres (cm)Inches (In)
C940 x 574 x 5.71.6 x 2.2
C1028 x 402.8 x 41.1 x 1.6
B6125 x 17612.5 x 17.64.9 x 6.9
B5176 x 25017.6 x 256.9 x 9.8
B4250 x 35325 x 35.39.8 x 13.9
E4280 x 40028 x 4011 x 15.75

View all standard dimensions in our Dimensions Chart