Cardboard Envelope Sizes: Standard Dimensions & Use Cases

Board Backed vs Capacity Cardboard Envelopes

Cardboard envelope sizes split into two systems: board backed formats built for flat documents, and capacity formats with an expandable spine for slightly bulkier contents. The two categories can look similar on a size chart, but picking the wrong one can mean a bent corner, a bowed spine, or a document that arrives creased. Most buyers only spot the difference after a shipment goes wrong.

Size also affects postage. An envelope larger than the contents need can push a parcel into a higher dimensional weight charge, while one that's too tight risks damaging the contents or forcing an extra fold they weren't designed to take. Matching the format to the shipment before you order avoids that trade-off entirely.

Globe Packaging stocks board backed and capacity envelopes across all standard sizes, so switching formats for a different shipment doesn't mean sourcing from a new supplier.

Standard Cardboard Envelope Sizes and Their Dimensions

Cardboard envelopes follow two main sizing frameworks: the ISO C-series (aligned with standard paper sizes) and capacity or rigid envelope formats sized around common item types like CDs, A4 documents, and books. Here's a breakdown of the most widely used sizes and where each one fits.

1. C4 Board Backed Envelopes (324 x 229 mm)

The board backing ensures that even heavier document stacks won't cause the envelope to bow or bend.

Stepping up in size, the C4 board backed envelope measures 324 x 229 mm, which is large enough to hold a full A4 sheet completely flat with no folding required. This makes it the go-to choice for legal documents, architectural drawings, contracts, and any professional correspondence where presentation matters.

Use Cases

• Full A4 documents sent flat

• Legal contracts and official correspondence

• Presentation folders and reports

• Large photographs (A4 size)

• Multi-page documents that shouldn't be folded

2. C5 Board Backed Envelopes (229 x 162 mm)

C5 board backed envelopes are often used for A5 sheets or folded A4 documents.

The C5 board backed envelope measures 229 x 162 mm and is designed to hold an A5 sheet flat or an A4 sheet folded once. The rigid board backing runs along the back panel, preventing the envelope from flexing during transit. This is one of the most commonly used sizes in office environments for sending invoices, certificates, and correspondence that must arrive flat and unfolded.

Use Cases

• Single A4 documents folded once

• A5 brochures and leaflets

• Greeting cards and invitations

• Photographs (up to A5 size)

• Certificates that can be folded without issue

3. Capacity Envelopes: CD Size (180 x 180 mm)

The self-sealing closure and rigid construction make these ideal for media distribution and small product dispatch.

The CD capacity envelope measures 180 x 180 mm, a square format purpose-built for CDs, DVDs, and small square items. Unlike board backed envelopes, capacity mailers feature a spine that allows for some thickness, meaning they can hold a slim disc case alongside a single folded document or sleeve insert. 

While board backed envelopes keep everything flat, capacity envelopes accommodate items with some depth without losing structural integrity. For CDs or DVDs, this distinction matters significantly.

Use Cases

• CDs and DVDs (single or slim-cased)

• Small square prints or art cards

• Media distribution for businesses

• Software discs with accompanying inserts

4. Capacity Envelopes: A1 Size (235 x 180 mm)

The capacity construction means it can hold items with a small amount of depth,
including folded documents paired with a slim promotional item or product sample.

The A1 capacity envelope measures 235 x 180 mm and sits between the CD square format and the larger A2 size. It's slightly wider than the CD envelope, making it a practical choice for items that are too large for the square format but don't need the full footprint of an A2 mailer.

This size is particularly useful for businesses sending out branded materials, small catalogues, or product samples alongside a covering letter. The rigid board construction keeps everything presentable on arrival, which matters when first impressions count.

Use Cases

• Small catalogues or booklets

• Promotional materials with a slim insert

• Product samples with accompanying documents

• Photography prints in the A5-adjacent range

• Media packs for press or marketing use

5. Capacity Envelopes: A2 Size (334 x 234 mm)

For e-commerce businesses dispatching items like journals, thin paperback books,
or folded garments alongside a packing slip.

The A2 capacity envelope measures 334 x 234 mm, closely aligned with A4 document sizing but with the added depth of a capacity spine. This makes it one of the most versatile cardboard envelope formats available. 

The A2 capacity envelope can hold an A4 document flat alongside additional inserts, small products, or thicker materials that a standard board backed envelope simply couldn't accommodate. It offers the flat-mail protection of a rigid mailer with just enough internal volume to handle lightly bulky contents without crossing into box territory.

Use Cases

• A4 documents with accompanying inserts or samples

• Thin paperback books and journals

• Folded garments or fabric swatches

• E-commerce product dispatch with packing slips

• Multi-document packs and presentation materials

Standard Cardboard Envelope Sizes: Summary Table

Match the Envelope to the Job with Globe Packaging

Whether you're sending legal documents, media discs, or e-commerce orders, matching your envelope to the job is one of the simplest ways to protect your contents and control your postage spend. The size difference between a C5 and a C4, or between a board backed envelope and a capacity mailer, can make a real difference to how your mail arrives and what it costs to send.

At Globe Packaging, we stock a full selection of capacity cardboard envelopes in high-grade, protective quality, held in a 60,000 sq ft depot that keeps availability strong even during busy periods. With same-day dispatch on orders placed by 4 p.m., you can reorder the sizes you rely on and keep your mailing operation moving without interruption. Visit Globe Packaging to browse our full selection of cardboard envelopes. 

*Note: Product listings, prices, and delivery times shown are approximate and subject to change. Contact Globe Packaging for the latest information.