Letter Box Boxes: Die Cut, Crash Lock and PIP Mailers Compared

Letter box boxes are flat cardboard boxes sized for small orders that post through a door letterbox. The three main choices are Royal Mail PIP large letter boxes, die cut mailers and crash lock boxes, and each suits a different product and packing speed. The sizes here are the ones Pack Solution sells from Manchester.

Postage class depends mostly on thickness. A Large Letter can be no more than 20mm thick, and every PIP box is made to that depth. Royal Mail sets the current length, width and weight limits, so check them before you post.

Quick Picks: Letter Box Boxes for Small Orders

For flat, light orders at the Large Letter rate, pick Royal Mail PIP Large Letter Boxes. For small products that need a neat brown box with no tape, pick Die Cut Boxes Brown 070502. For fast packing of deeper orders, pick Crash Lock Boxes.

Best for flat orders at the Large Letter rate

Royal Mail PIP Large Letter Boxes

Die cut cardboard boxes made no deeper than 20mm, in five sizes from Mini to C4, supplied flat in packs of 50.

• 20mm deep, all five sizes
• Mini, C6, DL, C5 and C4
• Pack of 50, supplied flat

From £5.00 ex VAT (£6.00 inc VAT)

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Best for small orders packed without tape

Die Cut Boxes Brown 070502

Brown die cut postal boxes that fold together by hand with no tape needed to assemble, supplied flat in packs of 50.

• Assembles without tape
• Plain brown finish
• Pack of 50, supplied flat

£20.00 ex VAT (£24.00 inc VAT)

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Best for fast packing of deeper orders

Crash Lock Boxes

Cardboard boxes with an automatic base that locks as the box is opened, so only the top needs closing.

• CL-A (100 x 100 x 70mm) to CL-K (426 x 300 x 300mm)
• No tape on the bottom
• Sold per box, minimum 5 per size

From £0.59 ex VAT (£0.71 inc VAT)

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Key Facts

• PIP boxes are die cut cardboard, 20mm deep, in Mini (101 x 101 x 20mm), C6 (163 x 112 x 20mm), DL (218 x 108 x 20mm), C5 (229 x 159 x 20mm) and C4 (325 x 225 x 20mm).
• Every PIP size comes in a pack of 50 boxes, supplied flat.
• The 070502 brown die cut box assembles without tape and comes flat in a pack of 50.
• Crash lock boxes run from CL-A (100 x 100 x 70mm) to CL-K (426 x 300 x 300mm), sold per box with a minimum of 5 per size.
• The C4 PIP box is larger than A4 (210 x 297mm), so an A4 print or document lies flat inside.
• Orders placed by 2pm Monday to Friday are dispatched the same working day, and Royal Mail Tracked 48 is free with no minimum.

What Are Letter Box Boxes?

Letter box boxes are thin cardboard boxes made to slip through a letterbox. Sellers also call them letterbox boxes or large letter mailing boxes, and the shared idea is a box shallow enough to slip through a letterbox.

A flat box gives a small product more protection than a paper envelope, which matters for jewellery, cosmetics, phone accessories and slim books. It also looks tidier when a customer opens it.

Not every box on this page is a Large Letter box. Only the PIP range is built to the 20mm limit. The die cut 070502 and the crash lock range are small parcel boxes, useful when your product is deeper than a letterbox allows. Picking the right one starts with the thickness of the packed item.

Large Letter Boxes: Royal Mail PIP Sizes

Royal Mail PIP large letter boxes are die cut cardboard boxes no deeper than 20mm, so you can post at the Large Letter rate instead of the dearer Small Parcel rate. Pack Solution supplies five sizes named after envelope formats: Mini, C6, DL, C5 and C4.

Each box folds by hand from a flat blank and every size is sold in packs of 50. The flat packs store easily, which suits a seller who posts a few dozen orders a week. If you send hundreds of large letters, email sales@packsolution.co.uk about trade pricing.

Which A4 Boxes Fit Flat Documents and Prints?

The C4 PIP box (325 x 225 x 20mm) is the flat option, and it is larger than A4 (210 x 297mm), so an A4 document or print fits flat. For a deeper A4 parcel, the CL-J crash lock box (426 x 300 x 150mm) takes an A4 item flat, though at that depth it is a parcel, not a Large Letter.

These a4 boxes suit different goods. The C4 PIP box handles prints, thin clothing and paperwork that you want protected on all sides. CL-J suits A4 items with some thickness, such as a folder with a product enclosed.

When the contents only need to stay uncreased, an envelope can be enough. Board Back Envelopes (Do Not Bend) have a stiff board back and a printed Do Not Bend warning. The C4 size is 324 x 229mm and comes in boxes of 125. C5 (229 x 162mm) is also 125 to a box, and C6 (162 x 114mm) comes 250 to a box. They keep certificates, photographs and calendars flat. They do not give the crush protection of a box, so choose a PIP box for anything that could be dented.

Best for flat A4 documents and photos

Board Back Envelopes (Do Not Bend)

Envelopes with a stiff board back and a printed Do Not Bend warning, so contents arrive flat.

• C4 (324 x 229mm) and C5 (229 x 162mm), 125 per box
• C6 (162 x 114mm), 250 per box
• Printed Do Not Bend warning

From £12.00 ex VAT (£14.40 inc VAT)

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Die Cut Boxes 070502 for Small Orders

The 070502 is a brown die cut postal box that folds together by hand with no tape on the base. It comes flat in packs of 50 and suits online sellers, gift shops and crafters posting small orders.

The folds lock the box shut, which saves tape and time at the packing bench. A plain brown finish takes a label, a stamp or a branded sticker well. Because it is one model, reordering means quoting 070502 and nothing else.

The product page gives no internal dimensions for this model. If your product is close to the limit, email sales@packsolution.co.uk before you order and ask for the exact size. Unused items can be returned within 30 days of delivery, but a quick check first saves the postage.

Choose the 070502 when you post small products often and want a quick, tidy box. Choose a PIP box when the Large Letter rate matters, and a crash lock box when the product is deeper or heavier.

Crash Lock Boxes for Deeper Orders

A crash lock box has an automatic base that locks into place as you open the box, so it assembles in seconds with no tape on the bottom. You only close the top. That cuts tape use and packing time on busy days.

The range runs from CL-A (100 x 100 x 70mm), which suits jewellery, small cosmetics and samples, to CL-K (426 x 300 x 300mm), the deepest size. CL-C (180 x 100 x 50mm) works for long, narrow items such as tubes or boxed accessories. CL-F (290 x 208 x 95mm) takes an A5 item (148 x 210mm) flat with room to spare.

Crash lock boxes are sold per box with a minimum of 5 boxes per size, and the price per box drops as you buy more. That makes it easy to test a size before you commit to a bigger order. Measure your product first, then allow room for any wrap or void fill.

Letter Box Boxes Compared

PIP boxes are the only range here built to the 20mm Large Letter depth. The 070502 and crash lock boxes suit small parcels, so compare the depth column first.

A flat product that must go at the Large Letter rate belongs in PIP. A boxed gift or a deeper item belongs in a crash lock box. A small product that fits a plain brown box belongs in the 070502.

Large Letter or Small Parcel?

A parcel goes at the Large Letter rate only if the packed item stays within the Large Letter size limits, and thickness is the one most boxes fail. Every PIP box is 20mm deep, so it meets the depth limit before you add the product.

Our large letter and Royal Mail PIP guide covers the sizing rules in more detail. If you are comparing a box with a soft option, padded envelopes vs postal boxes shows when each wins. For general box choices see postal boxes and Royal Mail sizes, and for the smaller end of the range read small cardboard boxes: sizes and uses.

How to Choose a Letter Box Box

1. Pack the product with its wrapping and measure the thickness.
2. If it is 20mm or less, pick the PIP size whose length and width are larger than the product.
3. If it is thicker, move to the 070502 or a crash lock size with room for void fill.
4. Check the current Royal Mail limits for the service you plan to use.
5. Order a pack, test the fit with a real order, then reorder in volume.

Letter Box Boxes Checklist

• Measure the packed item at its thickest point, not the bare product.
• Choose a PIP box for anything that must stay within 20mm.
• Use the C4 PIP box or CL-J when an A4 item needs a box.
• Use Board Back Envelopes when flat contents only need to stay uncreased.
• Keep one pack of your most common size in stock, and add a second size for the odd order.
• Order by 2pm Monday to Friday for same-day dispatch.

Choosing Your Letter Box Boxes

For Large Letter postage, buy PIP boxes in the size that matches your product. For small parcels, the 070502 and crash lock boxes cover the rest. Browse every cardboard option in our boxes collection, or look at envelopes for flat documents. Delivery details are on the shipping policy page.

Frequently Asked Questions

What are letter box boxes?

Letter box boxes are flat cardboard boxes shallow enough to post through a door letterbox. Royal Mail PIP large letter boxes are the clearest example: all five sizes are 20mm deep and come in packs of 50. Other boxes, such as crash lock boxes, are deeper and post as small parcels.

What size are large letter boxes?

Our large letter boxes are 20mm deep in every size. Mini is 101 x 101 x 20mm, C6 is 163 x 112 x 20mm, DL is 218 x 108 x 20mm, C5 is 229 x 159 x 20mm and C4 is 325 x 225 x 20mm. Check Royal Mail for current length, width and weight limits.

Which of the large letter mailing boxes fits A4?

The C4 PIP box measures 325 x 225 x 20mm, which is larger than A4 (210 x 297mm), so an A4 print or document lies flat inside. The C5 box (229 x 159 x 20mm) fits A5 items (148 x 210mm), such as slim books and DVDs.

Do the 070502 die cut boxes need tape?

No. The brown 070502 die cut boxes fold together by hand and assemble without tape. You can still add a strip of tape or a label across the lid for extra security. They are supplied flat in packs of 50, so a pack stores easily until you need it.

What is the smallest and largest crash lock box?

The smallest listed crash lock box is CL-A at 100 x 100 x 70mm and the largest is CL-K at 426 x 300 x 300mm. They are sold per box with a minimum order of 5 boxes per size, and the price per box falls as your quantity rises.

How fast can I get letter box boxes?

Orders placed by 2pm Monday to Friday are dispatched the same working day from Manchester. Royal Mail Tracked 48 is free on every order with no minimum, and usually arrives 2 to 3 working days after dispatch. Unused items can be returned within 30 days of delivery.

Shop for This Job

• Cardboard Boxes
• Envelopes

Related Guides

• Postal Boxes Guide: Sizes, Royal Mail Bands and Which Box to Buy
• Small Boxes: Cardboard Sizes And Uses For Posting Small Items
• Large Letter Boxes: Sizes, Limits and What Fits
• Padded Envelopes vs Postal Boxes for Small Items

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