custom large letter boxes

Sellers use custom large letter boxes to post slim products within the Royal Mail large letter size and weight limits while adding their own print and a fit that suits the item. Ordering custom large letter boxes in your exact size reduces movement inside the pack, keeps the parcel slim and helps each order arrive through the letterbox where the design allows.

The size rules behind custom large letter boxes

Royal Mail classes an item as a large letter when it measures no more than 35.3cm in length, 25cm in width and 2.5cm in thickness, with a weight limit of 750g for most services. Those are external measurements of the finished, packed item, so the box walls, the product and any insert or wrap all count. A box designed close to the limit leaves very little margin, so most sellers work a little inside it to allow for board thickness and packing variation.

Check the limits again before you commit to a size on the Royal Mail size and weight guidance page, because services and limits can change. If your packed item goes over the thickness or weight limit it moves into the small parcel band, which changes the postage you pay. Compare standard formats in our large letter postal boxes range before deciding whether a custom size is worthwhile.

What sellers post in this format

Slim and fairly flat goods suit large letter boxes best: greeting cards and stationery, books and magazines, phone cases and small electronics accessories, cosmetics compacts, jewellery in slim gift boxes, art prints and documents that must not bend. The rigid walls of a box protect contents far better than a paper envelope when items pass through sorting equipment and letterboxes.

Protecting slim items without adding bulk

Use a shallow insert, a card stiffener or tissue to stop the product sliding, and keep padding thin so the packed depth stays within the limit. Seal the box securely so the lid cannot lift and catch. Our letterbox postal boxes and A5 postal boxes show how shallow formats are arranged for common paper and product sizes.

Print and board choices for a custom run

Most large letter boxes are made from corrugated board with a fine flute, which gives a slim profile with useful crush resistance and a good print surface. Kraft board gives a natural look, and white board gives brighter colour for branded designs. Print your logo and a short message on the lid, and consider a simple inside print with a thank you note or reorder details. Keep artwork clear of fold lines and the area where the address label will sit.

When a standard size is the smarter choice

If a stock C4, C5 or DL style box already fits your product with a small margin, a standard size is usually quicker to reorder and simpler to manage. A custom size earns its place when your product sits between standard sizes, when you post high volumes and postage savings repeat on every order, or when the fit itself protects a fragile slim item. The C4 postal boxes page is a useful benchmark for A4 sized contents.

Ordering your custom size

Custom Postal Boxes manufactures in Wolverhampton with free design support, low minimum order quantities and free UK delivery. Pricing depends on size, material and quantity and is confirmed by quote, with no fixed prices listed. Send the internal size you need, your packed weight and your artwork, then contact the team for a quote and mention that the pack must stay within the large letter band.

FAQs about large letter sizing and print

What is the maximum size for a Royal Mail large letter?

The maximum is 35.3cm long, 25cm wide and 2.5cm thick, with a weight limit of 750g for most services. Measure the finished packed box, including board and contents, and leave a small margin below each limit.

What happens if my box is slightly too thick?

It will be classed as a small parcel rather than a large letter, which changes the postage cost. Keep padding thin, choose a shallow box and check the packed depth with the product and insert inside before you order in volume.

Can I print my branding on a custom large letter box?

Yes. Your logo, colours and messages can be printed on the lid and sides, with free design support to place artwork clear of folds and the label area. Approve the proof before production begins.

Which products suit large letter boxes best?

Flat and slim products suit them best, such as cards, stationery, prints, phone cases, slim books and compact cosmetics. If the product is thick, heavy or fragile in depth, a small parcel box will usually protect it better.