Cardboard Box Sizes Chart: Dimensions in Inches, mm and cm

Cardboard box sizes are listed as length x width x height, and the chart below gives every size we stock in inches, millimetres and centimetres. Use it to match a box to your item before you order, or to compare sizes across ranges.

Pack Solution sells four box ranges: single wall, double wall, crash lock and PIP Large Letter boxes. The chart lists only the sizes in those ranges. We do not cut boxes to custom sizes.

Quick Picks: Cardboard Box Sizes by Range

These three ranges cover most sizes, from small products to house moves.

Best for everyday orders and light moving

Single Wall Cardboard Boxes

Light corrugated boxes in 15 sizes, listed by internal length x width x height.

• 5 x 5 x 5" (127mm) to 24 x 18 x 18" (610 x 457 x 457mm)
• Includes the 450 x 350 x 160mm Small Parcel Max box
• Minimum 5 per size

From £0.35 ex VAT (£0.42 inc VAT)

Choose sizeView product

Best for heavy goods and house moves

Double Wall Cardboard Boxes

Heavy duty boxes with two layers of fluting, stiffer than single wall and better for stacking.

• 12 sizes, 9 x 6 x 6" to 24 x 24 x 24"
• Two layers of fluting
• Sold per box

From £0.59 ex VAT (£0.71 inc VAT)

Choose sizeView product

Best for small products packed in volume

Crash Lock Boxes

Boxes with an automatic base that locks as you open them, so there is no tape underneath.

• 10 sizes, CL-A (100 x 100 x 70mm) to CL-K (426 x 300 x 300mm)
• No tape on the base
• Minimum 5 per size

From £0.59 ex VAT (£0.71 inc VAT)

Choose sizeView product

• Single Wall Cardboard Boxes come in 15 sizes, from 5 x 5 x 5" to 24 x 18 x 18", listed as internal sizes.
• Double Wall Cardboard Boxes come in 12 sizes, from 9 x 6 x 6" to 24 x 24 x 24".
• Crash Lock Boxes come in 10 sizes, from CL-A (100 x 100 x 70mm) to CL-K (426 x 300 x 300mm).
• Royal Mail PIP Large Letter Boxes are 20mm deep, from Mini (101 x 101 x 20mm) to C4 (325 x 225 x 20mm).
• The 17.7 x 13.7 x 6" single wall box is 450 x 350 x 160mm, the Royal Mail Small Parcel maximum.

How to Read Cardboard Box Dimensions

Box dimensions always run length x width x height. Length and width describe the opening, with length the longer side, and height is the depth from the opening to the base.

So a 12 x 9 x 6" box has an opening of 12 by 9 inches and is 6 inches deep. Turn the same box on its side and it looks different, but the listed carton box dimensions do not change, because they describe the box with its flaps at the top.

Check whether a size is internal or external. Internal sizes tell you what fits inside. External sizes are larger by the thickness of the board on each side, which matters when you are working to a postage limit. Our single wall sizes are listed as internal measurements.

Single Wall Cardboard Box Sizes

Single wall boxes are the everyday range, with 15 sizes from small cubes to large moving boxes. They are light, which helps with postage weight, and suit most e-commerce orders.

Single Wall Cardboard Boxes are listed by internal size in this chart, with a minimum of 5 boxes per size.

The 15.35 x 11.6 x 7.3" size is listed as Extra Strong single wall. The 17.7 x 13.7 x 6" box is sold as the Royal Mail Small Parcel Max. These shipping box sizes cover most orders a small online shop sends.

Double Wall Cardboard Box Sizes

Double wall boxes have two layers of fluting, so they are stiffer and stack better. Their 12 sizes run from 9 x 6 x 6" to 24 x 24 x 24".

Carton box sizes in this range overlap with single wall at 9 x 6 x 6", 12 x 9 x 6", 12 x 9 x 9", 12 x 12 x 12" and 24 x 18 x 18". Double Wall Cardboard Boxes are sold per box and suit heavy, fragile or high value goods, as well as moving house.

For heavy items, pick the smallest box that holds the item and its wrapping, so the finished box stays easy to lift. Large cardboard boxes sizes such as 24 x 18 x 18" suit bulky, light things like bedding and cushions rather than books. Our guide to large cardboard boxes covers the biggest sizes in more depth.

Crash Lock and PIP Box Sizes

Crash lock and PIP boxes are listed in millimetres. Crash lock boxes have an automatic base that needs no tape, and PIP boxes are 20mm deep for Large Letter post.

Crash Lock Boxes come in 10 sizes, coded CL-A to CL-K.

Royal Mail PIP Large Letter Boxes come in five sizes, all 20mm deep, in packs of 50.

Best for slim items sent as a Large Letter

Royal Mail PIP Large Letter Boxes

Die cut cardboard boxes made 20mm deep for the Large Letter band.

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

From £5.00 ex VAT (£6.00 inc VAT)

Choose sizeView product

Parcel Box Sizes Grouped by Use

Most orders fall into a handful of jobs, and each job has a few sizes that suit it. This table groups the chart by what you are sending.

Postal box sizes UK carriers price by depend on the outside of the parcel, so keep the band in mind when you choose between two close sizes.

How to Measure Your Item for a Box

Measure the item at its longest, widest and deepest points, then add room for wrapping. Pick the next box size up that fits all three figures.

1. Measure the item's length, width and height at the widest points, including handles or lids.
2. Add the thickness of any wrapping, usually a few centimetres on each side for fragile items.
3. Compare the three figures with the chart, matching the longest item side to the box length.
4. Choose the smallest box that clears all three figures.
5. If two sizes are close, pick the one that keeps you in the cheaper postage band.

Carriers check parcel box dimensions on the outside of the sealed box, so a box chosen to the millimetre for a postage band can tip over once its board and tape are added. Leave a little margin when you are close to a limit.

A box that is far too big lets the item move, so fill the space with void fill. A box that is too tight bulges, which weakens the corners and can push the parcel over a size limit. Our guide on what size box you need goes through the fitting step by step.

Converting Box Dimensions: Inches, mm and cm

One inch is 25.4mm, or 2.54cm. Multiply inch figures by 25.4 for millimetres, then divide by 10 for centimetres.

Many UK suppliers still name boxes in inches, while carriers and some product listings use millimetres or centimetres. The chart gives all three so you can compare without a calculator. Box dimensions cm figures are rounded to one decimal place, which is more precise than a tape measure on a packing bench.

Single wall and double wall boxes are both corrugated board, so the same standard corrugated box sizes turn up in both ranges, such as 12 x 12 x 12". Standard cardboard box dimensions are usually quoted in inches first, with millimetres in brackets.

There is no single official set of standard cardboard box sizes in the UK. Standard usually means round inch sizes such as 12 x 9 x 6 or 18 x 18 x 18, which most suppliers keep in stock. If you work in metric, the standard cardboard box sizes cm column in the chart is the one to use.

The board style matters as well as the size. Our sibling guide to slotted boxes and cardboard box styles explains standard flap cartons, crash lock and die cut boxes.

Cardboard Box Sizes Checklist

• Read every size as length x width x height.
• Check whether a size is internal or external.
• Measure your item at its widest points and add wrapping.
• Choose the smallest box that clears all three figures.
• Use double wall for heavy items and moving.
• Use PIP boxes for slim items posted as a Large Letter.
• Measure the sealed parcel before you buy postage.

Choosing From the Box Size Chart

Start with the job, find the matching group in the chart, then check your item against the internal sizes. Most sellers settle on three or four packing box sizes that cover nearly every order, plus a larger size for awkward ones. Write down the packing box dimensions you use most so reordering takes a minute. The boxes collection holds every size in this chart, with each listed in inches and millimetres.

Frequently Asked Questions

What are the most common cardboard box sizes?

Round inch sizes such as 12 x 9 x 6, 12 x 12 x 12 and 18 x 18 x 18 inches are among the most widely stocked. Our Single Wall Cardboard Boxes include 12 x 9 x 6 inch (305 x 229 x 152mm) and 12 x 12 x 12 inch (305mm cube), and our Double Wall Cardboard Boxes go up to 24 x 24 x 24 inches.

How do you read cardboard box dimensions?

Box dimensions are given as length x width x height. Length is the longer side of the opening, width is the shorter side, and height is the depth from the opening to the base. Our single wall sizes are internal, so your item and its wrapping must fit inside those figures.

What size is the largest Royal Mail Small Parcel box?

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. Royal Mail also sets a weight limit for the band and can change its limits, so check the current figures before posting.

Are there standard carton box dimensions in the UK?

There is no single official UK standard. Standard usually means a stock size cut in round inches, such as 12 x 9 x 6. Most UK suppliers list each size in inches with the millimetre figure alongside, and our chart gives centimetres as well.

How do I convert box dimensions from inches to cm?

Multiply each inch figure by 2.54 to get centimetres, or by 25.4 to get millimetres. A 12 inch side is about 30.5cm or 305mm. To go the other way, divide the centimetre figure by 2.54. Suppliers usually round to the nearest millimetre.

Which box sizes fit A4 paperwork flat?

An A4 sheet is 210 x 297mm, so it lies flat on any base at least that size. Our 12 x 9 inch single wall and double wall boxes have a 305 x 229mm base, which takes A4 flat. The CL-J crash lock box (426 x 300 x 150mm) also holds A4 flat.

Shop for This Job

• Cardboard Boxes

Related Guides

• What Is a Slotted Box? Cardboard Box Styles Explained for Packers
• What Size Box Do I Need? Postal Box Sizing Guide
• Large Cardboard Boxes Sizes Uses

← All buying guides