large letter postal boxes UK

large letter postal boxes UK are slim, rigid postal boxes made to keep flat items within the Royal Mail large letter size limit of 35.3 cm by 25 cm by 2.5 cm and a weight limit of 750 g. Using large letter postal boxes UK in the correct size keeps qualifying orders in the large letter band instead of the more expensive small parcel band. Custom Postal Boxes makes these boxes in Wolverhampton to sizes that suit your products, with low minimum order quantities and free UK delivery.

The large letter limit behind large letter postal boxes UK

Royal Mail measures the finished package, not the empty box, and it measures the thickest point. A large letter must be no longer than 35.3 cm, no wider than 25 cm, no thicker than 2.5 cm and no heavier than 750 g for standard services. Check the current Royal Mail size and weight guidance before you order, because services and limits can change and some tracked services treat weight differently.

That 2.5 cm thickness is the dimension sellers most often miss. The box wall, the product, any protective wrap and the bulge of a sealed flap all count. A box with an external height close to the limit leaves no room for contents that sit unevenly, so plan the internal depth around the thickest item in the order. Our large letter postal boxes are made with that finished measurement in mind.

What fits in a large letter box

Typical contents include A4 documents and catalogues, magazines, slim books, calendars, art prints, phone cases, flat clothing items and small electronics in slim packaging. If an order combines a flat item with something bulky, it will not qualify, however flat the box is. In that case pack the order as a small parcel from the start rather than forcing it into a slim box that arrives damaged.

Box design details that protect flat items

A large letter box should be rigid enough to stop bending, because a folded corner can ruin a print, book or document. Corrugated board with crush resistant edges works well, and a design that folds around the contents gives protection on all faces. Compare our letterbox postal boxes for orders that must also pass through a standard letterbox, and our A5 postal boxes for smaller flat items.

Packing to stay within the limit

Pack the order, seal it fully, then measure and weigh the finished package before you buy postage. Measure thickness at the thickest point, including any raised label or tape overlap, and weigh the box with everything inside. If you are close to a limit, change one variable, such as a thinner protective wrap, a lower profile box or one item fewer per package, and test again.

Keep contents flat and centred. A single item sliding to one end can create a thick point that fails the limit even when the rest of the package is slim. A light board insert or a paper wrap holds items in place without adding much thickness, and it also stops edges rubbing during sorting.

Print options for large letter boxes

Even a slim box has a large flat face for branding. A logo, web address and a short message print clearly on the lid, and print inside can carry returns guidance or an offer for the next order. Keep the delivery label area clear, place artwork away from fold lines, and use the free design support included with every order to check the layout before production.

Ordering large letter postal boxes UK

Ordering is quote based, because pricing depends on size, material and quantity. Send the size of your largest flat item, its thickness and weight, plus the quantity you need, through our contact page for a quote. Low minimum order quantities suit sellers testing the large letter route, and UK delivery is free. A sample size test with your real products is the safest way to confirm the finished package stays within the band.

FAQs about large letter postal boxes UK

What is the maximum size for large letter postal boxes UK?

The finished package must be no larger than 35.3 cm long, 25 cm wide and 2.5 cm thick, and no heavier than 750 g for standard Royal Mail large letter services. Always measure the packed and sealed box.

Why did my large letter get charged as a small parcel?

Usually because the finished package was thicker than 2.5 cm at its thickest point or heavier than the limit. Bulging flaps, uneven contents and thick protective wrap are common causes.

What products suit large letter postal boxes UK?

Flat items such as A4 documents, magazines, slim books, calendars, prints, phone cases and flat packed clothing suit these boxes, provided the packed weight and thickness stay within the limit.

Can large letter boxes be printed with my logo?

Yes. The flat lid gives a clear print area for a logo, web address and short messages. Free design support is included so the label area and folds are kept clear in the artwork.

How much do large letter postal boxes UK cost?

Pricing depends on size, material and quantity, so every order is quoted individually. Contact the team with your item dimensions for an accurate quote with free UK delivery.