Royal Mail Packaging: Boxes and Bags That Fit Royal Mail Size Bands

Royal Mail packaging is any box, bag or envelope chosen to fit one of Royal Mail's size bands, so the parcel goes at the rate you expect. The two bands that matter for most small sellers are Large Letter and Small Parcel. Get the packaging right and the postage follows from it.

Pack Solution is a packaging supplier and is not part of Royal Mail. We do not sell Royal Mail branded packaging, postage or stamps. We sell plain boxes, mailing bags and padded envelopes in sizes that line up with the Royal Mail bands.

Quick Picks: Royal Mail Packaging by Size Band

These three cover the Large Letter band, the Small Parcel band and soft goods.

Best for posting at the Large Letter rate

Royal Mail PIP Large Letter Boxes

Die cut cardboard boxes made 20mm deep, so slim items can go as a Large Letter.

• Five sizes, Mini (101 x 101 x 20mm) to C4 (325 x 225 x 20mm)
• Supplied flat
• Packs of 50

From £5.00 ex VAT (£6.00 inc VAT)

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Best for Small Parcel and larger orders

Single Wall Cardboard Boxes

Light corrugated boxes, including a 450 x 350 x 160mm box sized to the Royal Mail Small Parcel maximum.

• 15 sizes, 5 x 5 x 5" to 24 x 18 x 18"
• Sizes are internal
• Minimum 5 per size

From £0.35 ex VAT (£0.42 inc VAT)

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Best for clothing and soft goods

Grey Mailing Bags

Opaque grey polythene bags with a self-seal strip that add very little weight to a parcel.

• 16 sizes, 4 x 6" to 34 x 42"
• Self-seal, no tape needed
• Packs of 100, 50 or 25

From £2.90 ex VAT (£3.48 inc VAT)

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• Royal Mail PIP Large Letter Boxes are 20mm deep, from Mini (101 x 101 x 20mm) to C4 (325 x 225 x 20mm).
• The single wall 17.7 x 13.7 x 6" box is 450 x 350 x 160mm, the Small Parcel maximum.
• Single Wall Cardboard Boxes come in 15 sizes, sold with a minimum of 5 per size.
• Grey Mailing Bags come in 16 sizes from 4 x 6" (100 x 150mm) to 34 x 42" (850 x 1050mm).
• White Bubble Padded Envelopes run from EP1 (100 x 165mm) to EP10 (350 x 470mm).

Royal Mail Boxes Size Bands Explained

Royal Mail prices letters and parcels by size first and weight second. Your packaging decides the size band, so choose it before you think about postage.

For small sellers there are two key bands. A Large Letter is thin: Royal Mail's thickness limit has been 25mm, and there are length, width and weight limits as well. A Small Parcel can be up to 450 x 350 x 160mm, again with a weight limit. Anything bigger moves into the parcel bands above it.

Royal Mail Large Letter Boxes

Large Letter boxes are slim cardboard boxes that keep a parcel inside the Large Letter thickness limit. That usually makes the postage lower than sending the same item as a Small Parcel.

Royal Mail PIP Large Letter Boxes are die cut boxes made 20mm deep. They arrive flat and fold together, and come in packs of 50. PIP stands for Pricing in Proportion, the Royal Mail system that prices by size; the boxes take their name from it, though packaging firms make them.

The item plus any wrapping must fit inside the 20mm depth. If you have to force the lid shut, the parcel will bulge and may be charged as a parcel. Our guide to Large Letter PIP boxes covers fitting and folding in more detail.

Pick the PIP size by footprint once you know the depth works. An A5 notebook goes in the C5 box, a phone case fits the C6, and a set of pens suits the long DL. If an order has two slim items, lay them side by side in a larger box rather than stacking them, since stacking doubles the thickness. A packing slip folded once adds very little, but a thick leaflet or a gift card in a sleeve can be enough to stop the lid closing flat.

Royal Mail Small Parcel Boxes 450x350x160mm and Smaller

The largest box that fits the Small Parcel band is 450 x 350 x 160mm. Any box with all three measurements under those figures also fits, once the item is inside and the box is closed flat.

Single Wall Cardboard Boxes include a 17.7 x 13.7 x 6" box listed as Royal Mail Small Parcel Max, at 450 x 350 x 160mm. Single wall board is light, which helps keep the parcel inside its weight limit. Sizes are internal, so the outside of the box is a few millimetres larger.

Because the listed sizes are internal, measure the outside of a made-up box before you rely on it for a tight band. Boxes close to 160mm tall, such as 10 x 8 x 6" and 12 x 9 x 6", are the ones to check most carefully.

The 12 x 9 x 4" box suits A4 paperwork and folders, since an A4 sheet (210 x 297mm) lies flat on its 305 x 229mm base. The sibling guide on A4 paper size in cm, mm and inches gives the A4 figures if you post documents.

Royal Mail Bags: Mailing Bags and Padded Envelopes

Royal Mail does not ask for any special bag. A plain mailing bag works for any band, as long as the filled parcel meets that band's limits.

Grey Mailing Bags are opaque grey polythene with a self-seal strip. They are light and water resistant, which suits clothing, soft goods and books. There are 16 sizes, from 4 x 6" (100 x 150mm) to 34 x 42" (850 x 1050mm).

White Bubble Padded Envelopes have a bubble lining for small items that need some cushioning, such as jewellery, cosmetics and small electronics. They come in 10 sizes, EP1 to EP10, in boxes of 100.

Best for small items that need cushioning

White Bubble Padded Envelopes

White self-seal envelopes with a bubble lining for small, light products.

• 10 sizes, EP1 (100 x 165mm) to EP10 (350 x 470mm)
• Bubble lining
• Boxes of 100

From £8.00 ex VAT (£9.60 inc VAT)

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To pick a bag size, lay the item flat on the bag and allow a little room at the open end for the seal to close without strain. A bag that is too tight splits at the seams, and one that is far too big folds over itself and gets caught in sorting machines. For a regular product, try one bag size against the real item before you order a full pack.

Bags change shape when filled. A folded jumper in a 10 x 14" (250 x 350mm) bag can easily go over a Large Letter thickness limit, but it will usually sit well inside the Small Parcel band. A padded envelope with a slim item inside may still go as a Large Letter if it stays thin enough, so measure the filled envelope at its thickest point.

Measuring a Parcel for Royal Mail Parcel Box Sizes

Always measure the parcel after it is packed and sealed. Royal Mail parcel box sizes are checked against the finished item, not the empty box.

1. Pack the item with its wrapping and seal the box or bag.
2. Lay it on a flat surface and measure the longest side.
3. Measure the width across the widest point.
4. Measure the thickness or height at the thickest point, including any bulge.
5. Weigh the parcel on kitchen or postal scales.
6. Compare all four figures with Royal Mail's current limits for the band you want.

For Large Letters, a slot gauge or a strip of card cut to the thickness limit makes checking quick at a packing bench. Push each parcel through, and if it catches, it goes as a parcel.

Weight matters as much as size. A heavy item can push a parcel into a higher band even when it is small, so weigh the packaging you plan to use as well as the product. Light packaging such as mailing bags and single wall boxes leaves more of the weight allowance for the item itself.

Protecting Items Inside Royal Mail Packaging

A parcel that fits its band still needs to survive sorting. Fill the space around the item so nothing moves when you shake the box.

Wrap fragile items before they go in, and fill gaps with paper or other void fill so the item sits in the middle of the box, away from the walls. A box that rattles is a box where the contents hit the sides every time it is handled. Seal the top seam with packing tape along its full length and over the edges.

Inside a mailing bag, fold clothing neatly so the bag lies flat, and put anything that could be marked by moisture in its own clear bag first. Place the address label on the largest flat face, clear of seams and tape, so the barcode scans first time.

Choosing Royal Mail Boxes for Packaging Your Products

Start with the smallest band your product can fit in, then choose the packaging that keeps it there. Small royal mail boxes and slim envelopes are worth the effort only when the item is thin enough.

A few common cases:

• Flat, light items such as cards, prints and accessories go in a PIP box as a Large Letter.
• Small items that need cushioning go in a padded envelope, then measure to see which band applies.
• Clothing usually goes in a grey mailing bag as a Small Parcel.
• Fragile or boxed products go in a single wall box with wrapping, inside the Small Parcel size.
• Bulky orders go in a larger single wall box in the band above.

The style of box matters as much as the size for some products. Our sibling guide to slotted boxes and other cardboard box styles explains standard flap cartons, crash lock boxes and die cut boxes. When it is time to post, our guide to printing Royal Mail labels at home covers labels and printers.

Royal Mail Packaging Checklist

• Pick the size band first, then the packaging.
• Use 20mm deep PIP boxes for Large Letter items.
• Keep Small Parcels within 450 x 350 x 160mm.
• Remember single wall box sizes are internal.
• Measure and weigh the parcel after it is sealed.
• Check Royal Mail's current limits before buying in bulk.
• Buy postage from Royal Mail or your postage service.

Stocking Up on Packaging for Royal Mail

Most small sellers need one or two PIP box sizes, a Small Parcel box or two, and a mailing bag size for soft goods. Choose by the band you post in most often and keep a few of the next size up for awkward orders. The boxes, bags and envelopes collections hold every size mentioned here, and the Royal Mail postal box sizes stay the guide for which ones to buy.

Frequently Asked Questions

Do you sell Royal Mail boxes?

We sell boxes and bags sized for Royal Mail's bands, not Royal Mail's own branded packaging. Pack Solution is a packaging supplier and is not part of Royal Mail. Our Royal Mail PIP Large Letter Boxes are 20mm deep for the Large Letter band, and the 450 x 350 x 160mm single wall box matches the Small Parcel maximum.

What size are Royal Mail small parcel boxes?

The Royal Mail Small Parcel maximum is 450 x 350 x 160mm. Our Single Wall Cardboard Boxes include a 17.7 x 13.7 x 6 inch box at exactly that size. Smaller boxes such as 12 x 9 x 4 inch (305 x 229 x 102mm) also fit the Small Parcel band. Weight limits apply too, so check Royal Mail's current figures.

What are Royal Mail large letter boxes?

They are slim cardboard boxes made to stay under Royal Mail's Large Letter thickness limit. Ours are 20mm deep, in Mini, C6, DL, C5 and C4 sizes, sold in packs of 50. The finished parcel must also meet the Large Letter length, width and weight limits.

Are Royal Mail bags the same as mailing bags?

Royal Mail does not require a particular bag. Any mailing bag works if the filled parcel fits the size band you pay for. Our Grey Mailing Bags come in 16 sizes with a self-seal strip, and White Bubble Padded Envelopes add a bubble lining for small items.

Does the box size or the packed parcel size count?

The packed parcel counts. Royal Mail measures the finished item, including the box, any bulge from the contents and the label. A bag that looks flat when empty can be much thicker once filled, so measure after packing and before you buy postage.

Can I buy postage or stamps from you?

No. We sell packaging only. Buy postage from Royal Mail online, at a Post Office or through a postage service you already use. Our guide to printing Royal Mail labels at home explains how to print postage labels on your own printer.

Shop for This Job

• Cardboard Boxes
• Mailing & Polythene Bags
• Envelopes

Related Guides

• A4 Paper Size in cm, mm and Inches, Plus the Envelopes That Fit A4
• What Is a Slotted Box? Cardboard Box Styles Explained for Packers
• Large Letter Boxes: Sizes, Limits and What Fits
• Print Royal Mail Labels At Home

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