A Guide to Envelopes

Envelopes come in many different shapes and sizes with the most common being C4, C5, C6 and DL which are suitable respectively for paper sizes A4, A5, A6 and 1/3 of A4 or compliment slip size. As well as the standard type of envelope there are also Padded Bags, Protective Envelopes, Gusset Envelopes and Machine Envelopes available.

Envelope Types

C4 Size Envelopes

C4 envelopes are suitable for an unfolded piece of A4 paper. C4 envelope dimensions are 229mm × 324mm. The C4 envelope is a very common piece of stationery and can be found in most offices throughout the UK. C4 envelopes are commonly used for sending contracts, reports and brochures.

C5 Size Envelopes

C5 envelopes are suitable for an unfolded piece of A5 paper or an A4 sheet folded in half. C5 dimensions are 162mm x 229mm. C5 Envelopes are commonly used for mail shots or business letters.

C6 Size Envelopes

C6 envelopes are suitable for and unfolded piece of A6 paper or an A5 sheet folded in half. C6 dimensions are 114mm x 162mm. C6 envelopes are popular for personal use and fit postcards or greetings cards.

DL Size Envelopes

DL envelopes are suitable for a sheet of A4 paper folded twice. DL envelope dimensions are 110mm x 220mm. DL envelopes are commonly used for sending single page letters.

Board backed Envelopes

Board backed envelopes offer extra protection to important documents. They are typically made using stiff, heavy duty manila board which forms the back of the envelope. This board offers rigid protection for the paperwork inside. Board backed envelopes are used for sending Photo’s, employment documents, contracts and exam certificates.

Gusset Envelopes

Gusset envelopes are used for sending oversized items through the postal system. They come with either a ‘Block Bottom’ or ‘V-Shaped Bottom’ which allows the envelope to expand as required. As Gusset Envelopes typically hold larger items they are generally constructed out of heavyweight paper to help prevent tearing and damage in transit. Some uses for Gusset Envelopes are for the sending of Books, Magazines and Manuals.

Padded Envelopes and Bubble Bags

Padded bags and Bubble bags provide extra protection for delicate, valuable, bulky or heavy items. They are made of an outer layer of strong tear resistant paper and a bubble lined interior. Potential uses for padded bags and bubble bags are almost endless, however some common uses are for the mailing of CD’s, Books and Jewellery.

Media Mailers

Media mailers are envelope style products used for storing and posting CD’s and DVD’s. They can range from a simple envelope sleeve which is ideal for storage and protects against dust and static to corrugated cardboard which provides protection for postal transit.

Other Points to Consider

Envelope Styles


Pocket envelopes have the opening flap along the shortest edge.


Wallet envelopes have the opening flap along the long edge.

Envelope Seals

Peal and Seal

Peal and Seal is the easiest way of sealing an envelope. Simply pull away the covering strip to reveal a strong adhesive that seals instantly with a very strong bond.

Press Seal

Press seal envelopes have two strips of adhesive, one on the flap and one on the body of the envelope. These are pressed together to form a strong bond.

Gummed Seal

Gummed seal envelopes have a strip of adhesive on the flap of the envelope that becomes sticky when moistened.

Envelope Weight

Envelope paper weight ranges from 80gsm to 130gsm. Heavier weighted envelopes provide extra protection for the contents and are better suited to heavy items. They also present a better appearance to the recipient as they have a more substantial feel to them. If you are looking to make an impression opt for 100gsm or more.

Envelope Colour

A nice and simple choice of either White or Manilla (brown). Manilla are generally slightly cheaper than white and are ideal as a day to day envelope. White envelopes present a more professional image and are best used for important correspondence.

Windowed and Plain Envelopes

Widowed envelopes are generally more expensive than plain envelopes and allow you to display the address printed on the letter contained inside. Widowed envelopes present a better image so for important correspondence go with this option.

Envelope Sizes - ISO 269 Series

The international standard ISO 269 defines several standard envelope sizes which are designed for use with ISO 216 standard paper sizes.

Envelope FormatDimensions (MM)Dimensions (Inches)Recomended Use
C0 917 x 1297 36 1/8 x 51 1/16 Suitable for flat A0 size paper
C1 648 x 917 25 1/2 x 36 1/8 Suitable for flat A1 size paper or A0 size paper folded in half
C2 458 x 648 18 x 25 1/2 Suitable for flat A2 size paper or A1 size paper folded in half
C3 324 x 458 12 3/4 x 18 Suitable for flat A3 size paper or A2 size paper folded in half
C4 229 x 324 9 x 12 3/4 Suitable for flat A4 size paper or A3 size paper folded in half
C5 162 x 229 6 3/8 x 9 Suitable for flat A5 size paper or A4 size paper folded in half
C6 114 x 162 4 1/2 x 6 3/8 Suitable for A6 size paper or A4 size paper folded in half twice
C7/6 81 x 162 3 3/16 x 6 3/8 Suitable for one third A5 size paper
C7 81 x 114 3 3/16 x 4 1/2 Suitable for A7 size paper
DL 110 x 220 4 5/16 x 8 11/16 Suitable for one third A4 size paper

Royal Mail Pricing in Proportion (PIP) Initiative

The Royal Mail introduced the Pricing in Proportion Initiative in August 2006 to rebalance its prices. Pricing in proportion means that postage prices will be based on the size, shape and weight of mail so that they better reflect the costs of collecting, sorting and delivering. In practice, it will be the same price or cheaper to send smaller items whereas the pricing for larger or bulky items will rise.

Under PIP mail is split into three categories, Letter, Large Letter and Packets.

Mail SizeMaximum ThicknessWeightsContent Would Include
Letter, Size not to exceed 240mm x 165mm This size is larger than A5 (half a sheet of standard paper). 5mm 0-100g Most letters, postcards, bills and statements, some brochures and catalogues, most birthday cards.
Large Letter, Size not to exceed 353mm x 250mm. This size is larger than A4 (a standard sheet of paper). 25mm 0-100g 101-250g 251-500g 501-750g Large letters (containing unfolded sheets of standard paper). Most brochures, catalogues and company reports, some magazines. CDs and DVDs. Most larger birthday cards. Most magazines.
Packet Any 0-100g 101-250g 251- 500g 501-750g 751-1000g VHS cassettes, books, some magazines and catalogues, parts and samples, prints and posters in large or cylindrical packaging.

PiP prices, applicable from 4 April 2011.

Mail FormatWeightFirst Class StampsFist Class Meters/AccountSecond Class StampSecond Class Meters/Account
Letter 0-100g 46p 39p 36p 28p
Large Letter 0-100g 75p 55p 58p 44p
Large Letter 101-250g 109p 79p 92p 65p
Large Letter 251-500g 146p 110p 123p 90p
Large Letter 501-750g 207p 160p 176p 130p
Packet 0-100g 158p 136p 133p 114p
Packet 101-250g 196p 169p 172p 148p
Packet 251-500g 248p 190p 216p 159p
Packet 501-750g 305p 236p 261p 192p
Packet 751-1000g 371p 286p 315p 231p
Packet 1001-1250g 490p 398p n/a n/a
Packet Each additional 250g or part thereof +76p +70p n/a n/a


Carl Barton is a director of Office Allsorts who has worked in the office products industry for 15 years.

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