For an online-only sweet shop, how something fits through a letterbox is a genuinely practical question, not a quirky one — it decides whether a gift lands on a doormat the next morning or has to wait in for a courier.
The size that actually matters
Royal Mail doesn't publish one official "letterbox size" as such; the figure that matters is the Large Letter band, which covers anything up to 353 x 250 x 25mm and 750g. That 25mm — roughly two and a half centimetres — is the dimension that decides almost everything, since length and width have a reasonable amount of room to work with, but height is tight by comparison.
Why the margin matters more than the maximum
Packaging suppliers generally build in a tolerance of around 10mm either way on manufactured boxes, which means a box sold as exactly 25mm thick can occasionally come out slightly over on a given production run. Letterbox-friendly packaging that's designed right up to the legal limit, rather than comfortably under it, risks tipping into the next size and cost band on a technicality. Good letterbox packaging aims a little short of the ceiling rather than exactly at it.
What that means for sweets specifically
The 25mm height limit effectively rules out anything in a rigid tub, a glass jar, or a bottle, and anything in a bag bulky enough that it can't be pressed reasonably flat. It favours flatter formats instead: bagged pick 'n' mix, boxed chew bars, and card-backed multipacks all compress down to something that can realistically clear a quarter-inch letterbox gap. A 3kg bulk bag or a sweet tub, by contrast, is never going to be a letterbox item — it's built for volume, not for squeezing through a front door slot.
What ships this way from us
Our Share Bags and Multipacks & Cases are generally the best fit for letterbox-sized formats, along with smaller Pick 'n' Mix bags. Bulk Bags and Sweet Tubs are built around volume rather than letterbox dimensions, so those go out as a standard parcel rather than through the letterbox slot.
Frequently asked questions
What size does a parcel need to be to go through a letterbox?
Royal Mail's Large Letter band: up to 353 x 250 x 25mm and 750g.
Why does 25mm thickness matter so much?
Manufacturing tolerances of around 10mm either way mean packaging designed right at the limit can occasionally come out over it.
Does letterbox-sized post affect what can be included?
Yes — it rules out rigid tubs, bottles and bulky bags in favour of flatter formats like bagged sweets and boxed chews.
What does Supreme Sweets ship in letterbox-friendly formats?
Share bags, multipacks and smaller pick 'n' mix bags; bulk bags and tubs go out as standard parcels instead.
Source: Royal Mail Large Letter size and weight guidance, via packaging industry summaries.