The L × W × D convention
Packaging dimensions are written in a fixed order, always measured from the opening of the box:
- Length (L): the longer side of the opening.
- Width (W): the shorter side of the opening.
- Depth (D): the distance at right angles to the opening, from the opening to the bottom. Some suppliers call it height (H).
The opening decides everything. On a tuck-end carton the opening is at the top, so depth is the tall side: a perfume carton might be 50 × 50 × 120 mm. On a roll end tuck top mailer the opening is the lid, so length and width are the large footprint and depth is the shallow height, for example 220 × 160 × 60 mm. The same three numbers in a different order describe a completely different box.
Inside vs outside dimensions
Inside dimensions (also called internal dimensions) are the space available for the product. Outside dimensions are what the box measures externally, which matters for shipping rates, shelf space and fitting cartons into a master case.
The difference is the board itself. Each wall adds its thickness, so as a rough guide the outside is about two board thicknesses larger per dimension. On slotted shipping boxes the depth grows more, because the top and bottom flaps stack on top of each other. With thin carton board (around 0.4 mm) the difference is small; with double-wall corrugated (around 6–7 mm) it can be well over a centimetre.
Unless your printer says otherwise, specify inside dimensions. DielineKit takes inside dimensions and adds board allowances from the caliper you enter; the caliper guide explains the maths.
How to measure your product
- Measure the product at its widest points, including caps, pumps, handles and anything that sticks out.
- Decide which face goes through the opening. That face gives length and width; the other measurement is depth.
- Add clearance. For a snug folding carton around a rigid product, 1–3 mm on each dimension is typical; soft or irregular items may need more. For shipping boxes, add the thickness of inserts or void fill on every side.
- Round to a practical figure, such as the nearest 0.5 mm or 1/16 in.
- Prototype: print the dieline at 100% on card, fold it, and test the fit before ordering. Or fold it in the 3D simulator first.
Common measuring mistakes
- Mixing the order: giving width before length, or depth first, so the box opens on the wrong face.
- Sending outside dimensions as inside ones, so the box is too small by the board thickness.
- Measuring the product but forgetting inserts, trays, or a leaflet folded inside.
- Mixing units. Pick millimetres or inches and use them for every dimension and the caliper.
Start from a standard size
If your product is a common format, such as a 30 ml dropper bottle, a candle jar or a phone accessory, start from a standard size template and adjust from there.