Basics3 min readUpdated Nov 13, 2026

Box dimensions

A box size is three numbers, and the same three numbers can mean two boxes of different sizes. It depends on whether they measure the inside or the outside, and on which side each one is.

We measure the inside

On our boxes each size runs from one creaseCrease A fold line pressed into board so it bends cleanly, also called a score. Dashed green on our dielines. to the next, so it measures the space inside. The FEFCO codeFEFCO code A four-digit code for a corrugated box style from the FEFCO catalogue, such as 0201 for the regular slotted carton. It names the shape, not the size. also gives box sizes as inside sizesInside dimensions A box's sizes measured inside, from crease to crease. This is what you type on our boxes, and what box makers quote.. Start from your product, not from the box: measure it and add a little room, as our sizing help explains.

A thicker or thinner board leaves those creases where they are. What changes are the flap gaps, slots and lock tongues next to them. In thick corrugated the clear room inside is about one board thicknessBoard thickness How thick the board is, in mm, also called caliper. Type it into a box's dieline and the details around the folds follow it. less than the crease to crease size.

Length, width, height

Sizes are written in that order, length × width × height. In the FEFCO code the length and width are the sides of the opening, the longer one first, and the height runs from the opening down to the bottom.

So the length is a side of the opening, and a tall box can have a height bigger than both. On our boxes the ⓘ next to each size field names its side:

• Tuck box: length across the front panel, width front to back, height from bottom to top. On a tall box for a bottle, the height is the biggest number.
• Shipping box: length and width are the long and short walls, and the width is never more than the length. By default the flaps are half the width deep.
• Mailer box: length and width are the floor, height is how tall the walls stand.
• Pillow box: the odd one out. Its length runs tip to tip over the curved ends, and its height is how thick it is in the middle.

Millimetres or inches

We work in millimetres. If you think in inches, switch Units to in at the top of the Size section: the fields show inches, and so do the sizes on the drawing and in the PDF. The PDF stays at true size either way. A saved dieline or a shared link keeps millimetres underneath, so nothing moves when someone opens it in the other unit.

When you send a size to anyone, write the unit with it: 120 × 80 × 40 is a small box in millimetres and a huge one in inches.

When the outside matters

A shelf, an outer carton or a courier's size limit goes by the outside of the boxOutside dimensions A box's sizes measured outside, a little bigger than crease to crease. Shelves, outer cartons and couriers go by these., and that is bigger than the size you type: the board adds its thickness on every side, a little in thin card, more in corrugated. When the outside has to fit, your printer can work it out from the dieline and the board.

Couriers call the longest outside side the length, whatever the box maker called it. Many also turn those outside sizes into a dimensional weight and charge for it when it is more than the real weight, so a box that fits the product can be cheaper to send.

Bags and pouches

A bag or pouch has no board around it, so its sizes are the finished bag lying flat: width, height, and the gusset where there is one. Whether the width includes the seals changes from one kind to another, so read the measuring notes in that bag's guide in the Size charts.

Related guides