large letter cardboard boxes

large letter cardboard boxes are slim cardboard postal boxes made to stay within the Royal Mail large letter limits of 353 mm long, 250 mm wide, 25 mm thick and 750 grams, so flat items travel at large letter prices with far better protection than an envelope. Custom Postal Boxes manufactures large letter cardboard boxes in Wolverhampton with custom print, low minimum order quantities and free UK delivery.

Why large letter cardboard boxes save money on every order

Postage is one of the largest costs in online selling, and the gap between large letter and small parcel prices is paid on every single order. A product that can be packed within 25 mm thickness qualifies for the lower band for its whole life, which is why so many sellers of documents, prints, books, accessories and folded clothing design their packaging around this format from the start. The box format is often called a PIP box, after Pricing in Proportion, the Royal Mail system that prices by size and weight.

Cardboard earns its place over a padded envelope in three ways. It holds its shape, so contents cannot bend or crease. It protects corners and edges, which are where prints, books and documents actually get damaged. And it presents like a parcel rather than a letter, which matters when the item is a gift or a paid product rather than paperwork. Current formats and prices are listed on the Royal Mail prices page.

Sizes and formats in the range

The common large letter sizes

The largest format takes A4 items and is often called the C4 size. The C5 format holds A5 paper and smaller books, and the long DL format suits documents and slim accessories. The full range sits on the Large Letter Postal Boxes page, alongside Letterbox Postal Boxes and the C4 Postal Boxes range. For A5 contents, the A5 Postal Boxes page and our notes on A5 packaging boxes are worth reading together.

Measuring the finished parcel honestly

The limits apply to the parcel as posted, not to the empty box on your desk. Contents, board thickness, tape and any labels all count, and the measurement that matters is the thickest point of the finished parcel. Pack the item flat, avoid bulky filler, and check the closed box with a ruler before you commit to a print run.

Allowing for bulge and tape

Soft contents such as clothing push the centre of a slim box outwards, and a box that measures 23 mm at the edges can bulge past 25 mm in the middle. Leave a safety margin of a few millimetres when you choose a size, keep tape flat against the surface, and if a product sits close to the limit, test a packed sample through a sizing guide or template before ordering in quantity.

Weight needs the same honesty. The 750 gram limit includes the box itself, so heavier board and generous filler eat into the allowance for the product. Thin but rigid board is the sweet spot for this format, giving crush resistance along the flat faces while keeping both thickness and weight in hand.

Print, packing and ordering

Slim boxes still carry branding well. A logo and colour band on the lid is visible in the customer’s hands and in delivery photographs, and a short message inside the lid costs little and is read at the moment of opening. Pack flat items centrally, add a card stiffener for very flexible prints, and keep paperwork inside the box rather than taped outside where it can catch and tear.

Ordering is quote based, with pricing set by size, material and quantity. Low minimum order quantities suit sellers testing whether a product can move down a postage band, and free design support and free UK delivery are included as standard. Send your item dimensions through the contact page for a quote and the team will confirm the closest large letter size for your product.

FAQs about large letter cardboard boxes

What is the largest size for large letter cardboard boxes?

A Royal Mail large letter can measure up to 353 mm long, 250 mm wide and 25 mm thick. Large letter cardboard boxes are made just inside those limits, so the biggest styles hold A4 items, while smaller C5 and DL styles hold A5 paper and standard documents.

What is the weight limit for a large letter?

A large letter can weigh up to 750 grams including the box and any filler. Weigh the finished parcel rather than guessing, because board, tape and paperwork all count towards the limit, and a parcel that is overweight moves into the small parcel band.

What happens if my item is slightly too thick?

If the finished parcel is thicker than 25 mm, it cannot travel as a large letter and will be priced as a small parcel instead. Choose a shallower box, remove bulky filler and pack contents flat, because even a small bulge in the middle of the parcel counts at the thickest point.

Will large letter cardboard boxes fit through a letterbox?

Large letter cardboard boxes are designed around the large letter format, which passes through most standard UK letterboxes. Letterbox sizes do vary on older and unusual doors, so most senders think of the format as letterbox friendly rather than guaranteed for every single property.

Can large letter cardboard boxes be printed?

Yes. The lid and sides can carry your logo, colours and a short message, and print inside the lid is a popular touch for documents and gifts. Free design support ensures artwork avoids fold lines and the area where the postage label needs to sit.