Shallow boxes that fit Royal Mail’s Large Letter slot.
Typical price
£14 to £22
Why we pick it
- Typical price
- £14 to £22
- Works with
A slim box under 25 mm deep protects a small item better than an envelope and can still go at Large Letter postage. Measure the packed box before you buy postage.
Good for
- Jewellery, coins and graded cards
- Keeping postage cheap
Not for
- Anything thicker than 25 mm when packed
Our approved alternative for the same job: Small single-wall boxes, 25 pack
The guide
Each step in the order you'll need it.
Small, flat items an envelope would crush
Slim boxes suit you if you sell small, flat items that an envelope might crush: a lipstick or palette, a pair of earrings, a stack of graded cards, a paperback, a small crystal or a few coins in capsules.
Posting a handful of these each week on Vinted, Etsy and eBay, you'll get a few months from a 50 pack. At dozens a day, buy a larger case from a packaging supplier to bring the unit cost down.
External depth and board type
Royal Mail's Large Letter service has limits on length, width, thickness and weight. Read the current figures on Royal Mail's site, then choose a box whose outer depth leaves you a margin once it is folded and taped.
Confirm the listed dimensions are external. Internal sizes look generous, but the board adds a few millimetres on every side, which can push a box over the thickness limit.
Single-wall corrugated board with a crash-lock or tuck-in lid and a peel-and-seal strip works best. White board looks tidy for gifts and beauty; brown kraft hides scuffs better.
Packing a Large Letter box
Lay a sheet of tissue in the base, place the item flat and fill gaps with a little paper so nothing slides when you tip the box. Keep fill under the rim so the lid closes flat.
Close the lid, then run your packed box through a Large Letter template or measure it with a ruler before you buy postage. Weigh it on your postal scale at the same time.
Print a 100 by 150 mm label and fold any overhang onto the back, or use a smaller label if the lid is narrow. Stack flat-packed boxes upright near your bench so they stay square.
Other packaging and when to switch
Small single-wall boxes, 25 pack, are the fallback and fit anything too deep for the Large Letter slot. Move to them once the item goes over the thickness limit.
Die-cut postal boxes for small parcels, 50 pack, take bulkier items such as figures or trainers that still need a sturdy fold-up box. Kraft padded envelopes, D/1, 100 pack, cost less for soft or unbreakable items like clothing accessories.
Board-backed card mailers, C6, 100 pack, weigh and cost less for a single card in a toploader, while Small jewellery boxes, 50 pack, add a gift look inside this box.
Box cost against the postage you keep
A 50 pack at £14 to £22 works out at roughly 28p to 44p per box. That is more than a padded envelope, and less than a refund and a bad review for a crushed item.
Postage brings the bigger saving. Keeping a small order at Large Letter rates instead of Small Parcel rates often covers the box several times over, so measure each packed box until you know your usual items fit.
Common mistakes
Each one costs you money or reviews, and each has a fix.
- Check the external measurement against Royal Mail's limits. Boxes bought by internal depth can fold up too thick.
- Heavy void fill bows the lid and adds thickness; one layer of tissue or paper is enough.
- Test the packed box against a template before you pay Large Letter postage, or the buyer may face a surcharge.
- Several hardbacks can tip the weight over the Large Letter limit, so weigh before you choose the service.
- Flat packs stored on their side under weight warp. Stack them flat, or upright and loose.
Ranked in
Where it places in our rankings, and the reason.
Setups that use it
Complete kits this product is part of.
Questions
Will every box in this pack go as a Large Letter?
Only when the packed box sits within Royal Mail's current size and weight limits. Measure the closed box with your item in it, as the lid and tape add thickness.
Do I need tape?
Many slim boxes have a peel-and-seal strip. If yours do not, one short strip of tape over the lid holds it.
White or brown board?
White suits beauty, jewellery and gift orders where the unboxing counts. Brown kraft costs less and hides scuffs from sorting machines.
Can I post trading cards in these?
Yes. A toploaded card or a small stack in a team bag sits flat inside and gets more crush protection than a card mailer.
Should I add void fill?
A sheet of tissue or a little paper does it. Bulky fill makes the box too thick for Large Letter.
Alternatives
Other picks for the same job, cheaper and pricier.
Small jewellery boxes, 50 pack
A foam insert holds the piece still in the box. The box fits in a padded envelope, so most orders still go as a Large Letter.
Typical price£8 to £14
See on AmazonSmall single-wall boxes, 25 pack
Use these for boxed toys and beauty sets that a padded bag would crush, when double-wall board costs more than you need.
Typical price£8 to £14
See on Amazon12-inch LP record mailers, 10 pack
A folding board mailer holds one 12-inch record flat with stiffeners either side, so the corners and sleeve seams survive the sorting belts. Buy them if you sell vinyl every week; for a box set or a stack of records, use a small box with bubble wrap instead.
Typical price£10 to £18
See on AmazonDie-cut postal boxes for small parcels, 50 pack
These fold flat, close without tape and sit under the small parcel size of 45 × 35 × 16 cm. Pick a depth that fits your usual item with a little padding.
Typical price£18 to £28
See on Amazon