letterbox packaging

letterbox packaging is slim postal packaging designed to pass through a standard UK letterbox, so deliveries arrive safely indoors without the customer needing to be home. Custom Postal Boxes produces letterbox packaging in Wolverhampton in custom sizes with print, helping subscription brands, gift sellers and ecommerce shops cut failed deliveries while keeping products properly protected in a rigid, well fitting pack.

The idea is simple but the sizing has to be exact. A box that is a few millimetres too deep will not pass the letterbox, and a soft pack that bulges in the middle can fail even when its flat dimensions look right. Rigid slim boxes hold their shape, which is why they have become the standard choice for letterbox gifts, refills and subscription drops.

What counts as letterbox packaging

The packaging must stay inside the Royal Mail large letter limits and pass through the letterbox opening at the delivery address. Slim postal boxes, book style wraps and shallow mailer boxes all qualify when packed carefully. The letterbox postal boxes and large letter postal boxes pages show the core formats, while C4 postal boxes suit document sized contents.

Products that work well through the letterbox

Flat and fairly flat goods are the natural fit. Popular categories include beauty refills, vitamins and supplements in flat bottles, socks and underwear, stationery, seeds, pet treats, chocolate bars, tea and coffee pouches laid flat, and printed goods such as planners and activity packs. Curated letterbox gifts combine several slim items in one shallow box, arranged so the depth stays even across the whole pack.

Keeping the packed depth under control

Depth is where letterbox packaging succeeds or fails. Contents should be arranged in a single layer where possible, with taller items placed so the lid closes without pressure. Avoid stacking bulky items in the centre, because Royal Mail measures the thickest point of the finished parcel. A box with a defined shallow depth helps staff pack consistently, because the structure itself stops overfilling.

Even depth across the whole parcel

A useful bench test is to close the packed box and press gently along its length. If one area springs up higher than the rest, rearrange the contents before sealing. Even depth also helps the box slide through the letterbox smoothly at an angle, which is how many posties actually deliver larger letterbox packs.

Royal Mail large letter rules for letterbox packaging

Royal Mail large letters must not exceed 353 millimetres in length, 250 millimetres in width and 25 millimetres in thickness, with a weight limit of 750 grams. The Royal Mail size and weight guide sets out these limits alongside the parcel bands. Staying inside them keeps postage in the large letter band and avoids the surcharge and delay that follow when a parcel is measured as a small parcel instead. Weigh a fully packed sample, including tape, labels and any inserts, before you set your postage prices.

Letterbox sizes in real homes

Most modern UK letterboxes accept large letter sized packs, but older doors, narrow hallway boxes and some flat entrances are tighter. Brands that promise letterbox delivery usually design to the Royal Mail limits and note that very restricted letterboxes may still need a doorstep drop. Testing your packed box through a few real letterboxes, including an older wooden door, is a sensible check before launch.

Branding and ordering letterbox packaging

A shallow box gives you a wide flat lid, which is excellent print space for a logo and a clear one line promise. Inside print can carry refill reminders, loyalty messages or a QR style call to action in words. Custom Postal Boxes offers free design support, low minimum order quantities and free UK delivery, with pricing based on size, material and quantity because ordering is quote based. Request a quote through the contact page once you know your product layout, and compare custom subscription boxes if your letterbox offer runs on a monthly cycle.

Failed delivery cards frustrate customers and create support work, so the commercial gain from letterbox packaging is wider than postage alone. Orders land first time, perishable or time sensitive contents spend less time in depots, and customers reorder from brands whose deliveries simply fit their day. For wider duties on packaging placed on the market, the GOV.UK extended producer responsibility guidance is the official reference.

FAQs about letterbox packaging

What size is letterbox packaging in the UK?

It is sized to the Royal Mail large letter limits of 353 by 250 by 25 millimetres and up to 750 grams when packed. Staying within those limits means the parcel can be posted as a large letter and should pass through a standard UK letterbox.

What products can be sent in letterbox packaging?

Any product that packs flat or nearly flat, including beauty refills, flat packed clothing, stationery, seeds, pet treats, chocolate, tea, supplements and printed packs. Sets work well when items are arranged in one even layer so the depth stays below the limit.

Will letterbox packaging always fit every letterbox?

It fits most standard letterboxes when sized to Royal Mail large letter limits, but a small number of older or unusually narrow letterboxes are tighter. Testing a packed sample through real doors before launch gives you confidence in the delivery promise you make to customers.

Can letterbox packaging be branded?

Yes. The wide flat lid is ideal for a logo and short message, and the inside can carry refill reminders or loyalty notes. Free design support is included, so artwork is checked against the shallow structure before your boxes go into production.