c4 postage boxes

If you post A4 sheets that must arrive flat and uncreased, c4 postage boxes are the slim rigid boxes sized around an A4 page, typically about 320 mm by 230 mm inside with a shallow depth for large letter posting. Custom Postal Boxes supplies custom printed versions from Wolverhampton with low minimum order quantities, free design support and free UK delivery on quoted orders.

What c4 postage boxes are designed to do

A C4 envelope takes an A4 sheet without folding, and a C4 box does the same job with far more protection. Certificates, contracts, artwork prints, calendars and examination papers all lose value when a corner bends, and a rigid box prevents that in a way a paper envelope cannot. Schools, solicitors, print shops and training providers are regular users because their documents are the product, not just paperwork.

Our C4 Postal Boxes sit within the wider Large Letter Postal Boxes range, so if your item is thinner or smaller you can step down to a C5 or A5 format instead of paying large letter postage on an oversized pack. Matching the box to the paper size keeps both the product and the postage under control.

Staying inside Royal Mail large letter limits

A Royal Mail large letter can be no larger than 353 mm by 250 mm by 25 mm and no heavier than 750 g, as shown on the Royal Mail tracked services page. A well made C4 box keeps its outer dimensions and its packed weight inside those limits, including any board stiffener, sleeve or printed insert you add. Weigh one finished pack on kitchen scales before you commit to a postage service for a whole batch.

Why depth is the measurement that catches people out

Length and width rarely cause trouble with C4 post, but depth does. A catalogue, a framed print mount or a stack of certificates can quietly push a pack past 25 mm once the lid closes. Choose a box depth that closes without bulging, and if your contents sit close to the limit, move up to a small parcel box rather than risking surcharges or a returned item and an unhappy recipient.

Materials and print for document boxes

Most C4 boxes use single wall corrugated board or sturdy cardboard with a smooth outer liner that takes print cleanly. A plain white or kraft finish suits legal and educational posting, while full colour print turns the box into branded packaging for print sellers and photographers. Add your logo, a returns note or handling guidance such as a request to keep the pack flat, printed where the recipient will see it on opening.

Sellers who post a mix of sizes often combine C4 with A5 Postal Boxes for smaller documents, so each order travels in the smallest suitable box. That habit reduces void fill, keeps packs lighter and helps every parcel stay in the lowest postage format its size allows.

Packing A4 items well

Slide documents in squarely so corners reach the box corners without bending, and place any stiffener behind the full sheet rather than under one half. Close the lid without forcing it, and check the pack stays flat on a table with no rocking. If you include a compliment slip or a printed guide, put it on top so it is read first. For valuable certificates, note the recipient address clearly and consider a tracked service.

To order, send your document size, typical pack weight and quantity via our contact page for a quote. Pricing depends on size, material and quantity, and every order is quoted individually with free UK delivery and free design support included in the service.

FAQs about c4 postage boxes

What size are c4 postage boxes?

C4 boxes are made to hold A4 sheets flat, so internal sizes are typically around 320 mm by 230 mm with a shallow depth of about 20 mm. The A4 page itself measures 297 mm by 210 mm, which leaves a small margin so documents slide in without their corners bending or catching.

Do c4 postage boxes go as a Royal Mail large letter?

Yes, provided the packed box stays within 353 mm by 250 mm by 25 mm and under 750 g in total. That includes the documents, any stiffener and the box itself. If your contents push the pack over the depth or weight limit, it will be charged as a small parcel instead.

Can c4 postage boxes be printed with my logo?

Yes. The flat lid and base give a large clean print area for a logo, brand colours or handling instructions. Custom Postal Boxes offers free design support to position your artwork well, and low minimum order quantities mean print is practical even for schools, studios and small print shops.

What can I send in a c4 postage box?

Common contents include certificates, contracts, A4 prints, photographs, calendars, magazines and slim books. Anything flat and close to A4 size that would be damaged by folding or bending suits a C4 box. For thicker stacks or heavier books, choose a deeper small parcel box so the pack stays within postage limits.