c5 postage boxes

c5 postage boxes are slim postal boxes shaped around the C5 paper size, which takes an A5 sheet unfolded or an A4 sheet folded once, so documents, prints and flat goods travel with rigid protection. At Custom Postal Boxes, a project of Vertex Packaging based in Wolverhampton, these boxes are manufactured in house for UK businesses that want printed, correctly sized packaging with low minimum order quantities and free UK delivery.

Why c5 postage boxes suit large letter post

Royal Mail prices post by size as well as weight, and its large letter category allows items up to 35.3 cm long, 25 cm wide and 2.5 cm thick, weighing up to 750 g, as its Royal Mail guide to UK letter and parcel services sets out. A C5 box sits well inside those limits when its depth stays close to 20 mm, which keeps slim items in the cheaper large letter band instead of the small parcel band.

A flat envelope cannot protect corners, and a padded bag can still let prints bend. A shallow corrugated box holds its shape, spreads pressure across the whole item and presents your brand neatly when the customer opens it. Sellers of greetings cards, art prints, calendars, seed packets, face masks and slim books use this format because it fits through most letterboxes, so the customer does not need to wait in for a parcel.

What fits inside a C5 box

The C5 footprint is about 229 mm by 162 mm, so the usable space inside a box is a little smaller once board thickness is counted. A5 documents, A5 booklets, postcards in sleeves, small framed prints without deep frames and flat packed accessories all fit well. Measure your item with any sleeve or backing board included, and leave a small margin so the lid closes flat without bowing, because a bowed lid can push total thickness past the large letter limit.

Checking thickness before you post

Close the packed box, then measure its thickest point including tape and any label that wraps over an edge. If the total is close to 25 mm, reduce padding inside or choose a shallower box. Weigh the packed box to confirm it stays within 750 g.

Board, print and packing choices

Most c5 postage boxes use single wall corrugated board or stiff card with a fold over design that assembles quickly without much tape. A self seal strip speeds packing further and gives a clean finish. Our A5 postal boxes and large letter postal boxes cover the same posting job in plain and printed forms, and the postal boxes by size range helps you compare footprints if your products vary.

Printing the outside with your logo turns a regulated size into a brand asset, and printing inside the lid adds a thank you message or care note at no extra packing effort. Keep print away from the address label area so nothing competes with the delivery details. For fragile flat items, add a stiffener card rather than loose padding, because loose fill raises thickness and can move in transit.

C5 compared with C4 and DL sizes

C4 boxes take A4 sheets flat, so they suit certificates and documents that must not fold, while DL suits long slim items such as tickets and invitations. C5 sits between the two and matches the most common document and print sizes sold online. Choosing the smallest box that fits your item keeps postage in the lowest band available and reduces the void fill you need to buy and store.

Ordering c5 postage boxes from a UK maker

Buying from a UK manufacturer means the box is made to the size you agreed, rather than a near fit imported size that wastes space on every parcel. Custom Postal Boxes offers free design support, low minimum order quantities and free UK delivery, with ordering on a quote basis because pricing depends on size, material and quantity.

If you send several flat formats, standardising on C5 for the mid sized ones simplifies storage and packing benches. Tell us what you post, how many you send each week and whether you want print, through our contact page for a quote, and we will recommend a board grade and closure. Matching letterbox postal boxes are available for slightly deeper items that still need to fit through the door.

FAQs about c5 postage boxes

What size are c5 postage boxes?

They are shaped around the C5 paper size of about 229 mm by 162 mm, with a shallow depth of roughly 20 mm. Exact internal measurements vary a little with board thickness, so check the usable space against your item before ordering in quantity.

Do c5 postage boxes go as Royal Mail large letters?

Yes, provided the packed box stays within the large letter limits of 35.3 cm by 25 cm by 2.5 cm and 750 g. Keep depth low, avoid bulky padding and measure the closed box including tape to be sure it qualifies.

What products suit c5 postage boxes?

They suit A5 documents, greetings cards, art prints, calendars, slim books, seed packets and other flat goods that need rigid protection. Anything deeper than about 20 mm belongs in a small parcel box instead.

Can c5 postage boxes be printed with my branding?

Yes. Custom Postal Boxes prints logos and artwork on postal boxes made in house, and free design support is included. Pricing depends on size, material and quantity, so request a quote for your print design and order volume.