letterbox postal boxes

Slim and protective, letterbox postal boxes are shallow cardboard boxes made to fit through a standard letterbox and stay within Royal Mail large letter limits. Custom Postal Boxes manufactures them in Wolverhampton with custom print, low minimum orders and free UK delivery.

Why letterbox postal boxes suit large letter post

Royal Mail prices letters by size and weight, so a shallow box inside the large letter format can cost less to post than a small parcel. The large letter limit is 353mm long, 250mm wide and 25mm thick, with a maximum weight of 750g for standard services. A well fitted box keeps thickness even and avoids the bulge that pushes a parcel into a higher band. Weigh the finished parcel before you buy postage, and check the Royal Mail sending guidance if you are unsure which format your item falls into.

Sizes that buyers ask for most

Most orders follow familiar paper sizes. C5 boxes suit A5 items at about 229mm by 162mm, while C4 boxes hold A4 sheets flat at about 324mm by 229mm. DL sizes suit long slim items such as invitations, and smaller square formats suit jewellery. Our large letter postal boxes and C4 postal boxes show how these formats look in practice, and every size can be adjusted when your product sits between standard options.

How to measure your item before ordering

Lay the item flat and measure its longest side, widest side and thickness at the thickest point, including any pouch or backing card. Add a small amount of clearance so the item slides in without forcing the folds. If the total sits close to 25mm, pack flatter items on top, because a bulky seal can add the millimetres that change your postage band.

Materials and print choices for a neat finish

These boxes are usually made from corrugated cardboard or sturdy kraft board, giving far more protection than a paper envelope while staying light enough for letter post. Corrugated board cushions edges and resists crushing in sorting, kraft gives a natural look, and white board gives a clean surface for bright artwork. See the construction on our letterbox postal boxes range, where the shallow profile and neat folds are designed for letterbox delivery.

Print that turns a plain box into brand packaging

Custom print can carry your logo, brand colours, web address and a thank you message on the lid, with care wording printed inside. The lid is often the first brand surface the customer sees, so clear print matters more than dense artwork. Free design support is included before anything is made in house in Wolverhampton.

Packing advice for safe letterbox delivery

Place flat items centrally, wrap delicate surfaces in tissue, and use a shaped card insert when an item could slide. Seal every opening with strong tape and keep the address label on the largest flat surface. Avoid overfilling, because a domed lid can lift the packed thickness above the large letter limit. Cardboard can be recycled after use, and larger UK organisations should also read the GOV.UK guidance on extended producer responsibility for packaging to understand their reporting duties.

What these boxes carry well

Typical contents include jewellery, cosmetics in flat packaging, phone cases, greetings cards, certificates, paperback books, slim folded clothing and craft kits. The common thread is a product that is flat or can be presented flat without force. Fragile items still need individual wrapping, and the 750g weight limit includes the box itself.

Ordering from Custom Postal Boxes

Custom Postal Boxes is a project of Vertex Packaging, based in Wolverhampton, and every box is manufactured in house. Orders are quote based, so pricing depends on size, material and quantity, and low minimum order quantities suit short first runs. Free UK delivery is included. Send your measurements and print ideas through our contact page for a quote and the team will advise on size, board and finish.

FAQs about letterbox postal boxes

What is the largest size for letterbox postal boxes?

For Royal Mail large letter post, the finished parcel must be no larger than 353mm long, 250mm wide and 25mm thick, and weigh no more than 750g including the box. Most sellers choose a size with a small margin.

Will letterbox postal boxes fit through every letterbox?

They are designed to pass through a standard UK letterbox when the packed thickness stays within the large letter limit, but openings vary between properties, especially on older doors. Keeping the parcel flat and at or below 25mm thick gives it the best chance of being posted through.

Can letterbox postal boxes be printed with my logo?

Yes. The lid and outer panels can carry your logo, brand colours and web address, and the inside can carry care wording, social details or a thank you message. Free design support is included, and pricing depends on size, material and quantity, so you can request a quote before you commit to a full run.

Are letterbox postal boxes recyclable?

Yes. Cardboard letterbox boxes can usually be recycled with household paper and card collections once tape and labels are removed where practical. Choosing a box that fits the product closely also reduces waste, because a snug box needs less void filling material to keep the contents still in transit.

How many letterbox postal boxes do I need to order?

Low minimum order quantities apply, so new and small brands can order a short run to test a size or design before ordering more. Share your product dimensions, the board finish you prefer and an idea of quantity when you enquire, and you will receive a quote based on those details.