Almost every packaging mistake we see at quote stage traces back to a dimension given in the wrong order, or given as an exterior measurement when the supplier assumed interior. Both are easy to avoid once you know the convention.
The convention: length, width, depth
Face the box with its opening towards you and measure in this order:
| Dimension | Which edge | How to find it |
|---|---|---|
| Length | The longer side of the opening | Measure the longer of the two edges that form the open face |
| Width | The shorter side of the opening | Measure the shorter edge of that same open face |
| Depth | Front to back | Measure from the opening straight down to the base |
Depth is sometimes called height, which causes trouble because height suggests the box is standing upright. It is the same measurement either way: the distance from the opening to the bottom. Write it third and it will be read correctly.
A box written as 8 x 6 x 3 is eight inches along the opening's long edge, six across, three deep. Written as 3 x 6 x 8 it describes a completely different box, and it will be quoted as one.
Interior, not exterior
This is the one that costs money. Packaging dimensions are interior dimensions by default, because what matters is whether the product fits. Exterior dimensions matter for freight and pallet planning, and they are always larger by the thickness of the board.
| Board | Approx thickness | Added to each exterior dimension |
|---|---|---|
| Paperboard carton, 18pt | 0.46mm | Under 1mm total |
| E-flute corrugated | 1.6mm | About 3mm total |
| B-flute corrugated | 3mm | About 6mm total |
| BC double-wall | 6mm | About 12mm total |
On a small carton the difference is negligible. On a double-wall shipper it is over a centimetre in each axis, which is enough to change how many cartons fit a pallet layer.
Sizing a box around a product
Measure the product at its widest point in each axis, then add clearance. How much clearance depends on what the box has to survive.
- Rigid product, no protection needed: add 2 to 3mm per axis so it slides in without forcing
- Product with a paper or pulp insert: add the insert wall thickness, usually 3 to 5mm per side
- Fragile or glass: add enough for the insert to hold the item clear of every wall, typically 10mm or more
- Soft goods: measure folded to its final packed state, not flat
Too tight and the product will not go in on the packing line, or it bursts a seam. Too loose and it rattles, which looks cheap on arrival and increases damage in transit. If you are unsure, send the product dimensions and let us work the clearance out against the format.
Why an extra millimetre can cost real money
Parcel carriers bill on dimensional weight as well as actual weight, so a box that is larger than it needs to be is charged as if it were heavier. The same applies upstream: a carton sized without reference to a standard 48 x 40 inch pallet footprint often wastes a row per layer.
We check carton dimensions against pallet patterns at the dieline stage and flag where a small change fits an extra row. That change is free at design stage and keeps paying back on every freight invoice afterwards.
What to send us
Interior dimensions in length x width x depth order if you have them. If you do not, send the product dimensions and what goes around it, and we will size the box. Either way the dieline comes back free within 24 hours.