letterbox boxes UK

letterbox boxes UK sellers use are slim postal boxes designed to pass through a standard UK letterbox, so orders arrive safely even when the customer is out. Custom Postal Boxes, a project of Vertex Packaging in Wolverhampton, manufactures letterbox boxes UK businesses rely on for flat products, with low minimum order quantities, free design support and free UK delivery.

What letterbox boxes UK delivery depends on getting right

Two measurements decide success. The box must be slim enough for a letterbox opening, and the finished packed parcel should stay within postal size limits if you want large letter postage. Royal Mail large letter limits are 353 mm in length, 250 mm in width, 25 mm in thickness and 750 g in weight for the packed item, which is why most letterbox designs keep the depth close to 20 mm to leave room for board and tape.

Check the current service details on the Royal Mail guide to sending small parcels and letters before you commit to a size, because services and limits can change. Letterbox openings also vary between homes, particularly on older doors, so a sensible design does not push every dimension to its absolute maximum. A trial through a typical letterbox is a useful final check alongside a tape measure.

The products UK sellers post in letterbox boxes most often

Books, prints, greeting cards, documents, slim clothing, beauty refills, vitamins in flat packs, phone cases, jewellery in small cases and sample sets are all common. The shared features are a flat profile, modest weight and a need for more protection than an envelope gives. If a product can bend, choose a board grade that holds its shape, because a folded parcel may fail delivery even if it started within the size limit.

Why a snug internal fit protects flat products

Movement inside a slim box concentrates damage at corners and edges, which is exactly where prints, books and card products show wear. A snug fit, a thin protective sheet over delicate surfaces and secure corners will do more good than loose padding that pushes the box over the thickness limit. Pack a test order, seal it as normal and check the corners after handling it firmly.

Sizes, board choices and branding

Browse our core letterbox postal boxes and large letter postal boxes, check the postal boxes by size category for other footprints and consider A5 postal boxes for the most common paper size. Each route helps you match the box footprint to the product rather than forcing the product into an oversized carton.

Kraft board is a popular choice for a natural look and a strong surface for bold print, while white board gives cleaner colour for detailed artwork. Single wall corrugated board is widely used because it balances cushioning, stiffness and low weight. Print can be as simple as a logo on the lid, or a fuller design with an inside message that turns a practical delivery into a small branded moment.

Balancing postage savings with product protection

Staying in a lower postage category is valuable only if the product arrives in good condition. Returns and replacements quickly erase a small postage saving, so do not remove necessary protection just to save a few millimetres. Instead, choose a box designed for the category from the start, with board thickness and product size planned together, and review damage rates after the first batches are delivered.

Ordering letterbox boxes UK sellers can reorder with ease

Pricing depends on size, material and quantity, so letterbox boxes are supplied by quote rather than at a stated price. Share your product dimensions, packed weight, target postage category and expected order volume. Free design support can place your branding on the lid and check that no important artwork sits on a fold or near a locking tab.

Low minimum order quantities make it realistic to start with one best selling product, prove the fit and customer response, then extend the same approach to other flat lines. When you are ready, send your details through our contact page to request a quote and say whether the box must pass a letterbox, stay within large letter limits or do both, because those aims lead to slightly different designs.

letterbox boxes UK FAQs

What is the maximum size for letterbox boxes UK post as a large letter?

For Royal Mail large letter post, the finished packed parcel must be no larger than 353 mm by 250 mm by 25 mm and weigh no more than 750 g. Most letterbox boxes are designed a little below those limits so board, tape and contents still fit once the box is sealed.

Do letterbox boxes fit through every UK letterbox?

No single size fits every letterbox, because openings vary between properties and older doors can be smaller. Boxes designed within large letter limits and kept slim will fit most standard letterboxes, but delivery cannot be guaranteed for every individual door.

What should I do if my product is too thick for a letterbox box?

If the packed product exceeds the slim profile, use a small parcel box instead and set delivery expectations around parcel delivery. Forcing a thick product into a letterbox box risks damage, a failed delivery and a parcel that no longer qualifies for large letter postage.

Can letterbox boxes be printed with my branding?

Yes, letterbox boxes can be printed on the outside and often inside the lid, with your logo, colours and a short customer message. Share your artwork when you request a quote and free design support can check its position against folds and closures.