Almost every box sizing error traces back to one of two things: mixing up inside and outside dimensions, or forgetting that board has thickness. This page covers the measurement conventions, the effect of flute, and how to check your size against what shipping will cost.
The convention: length x width x depth, inside
Corrugated is measured length first (the longer of the two open edges), then width (the shorter open edge), then depth (the distance from the opening to the base). Those numbers describe the inside of the box, because the inside is what has to fit your product. Outside dimensions matter only for shipping, palletising and shelf space.
The gap between the two is the board. A single wall box adds roughly two board thicknesses to each of length and width, and to depth. It sounds trivial until you are palletising: a quarter inch per box, multiplied across a pallet layer, is the difference between a tidy stack and an overhang.
How much thickness each flute adds
| Flute | Approximate board thickness | Approximate addition to each outside dimension |
|---|---|---|
| E | About 1/16 inch | About 1/8 inch |
| B | About 1/8 inch | About 1/4 inch |
| C | About 3/16 inch | About 3/8 inch |
| A | About 1/4 inch | About 1/2 inch |
| BC double wall | About 5/16 inch | About 5/8 inch |
These are nominal figures used across the industry, and real board varies slightly by mill. For anything where the fit is tight, ask us to confirm the caliper of the exact board on your quote rather than working from the table.
Sizing your own box in four steps
- Measure the product at its widest point in all three directions, including any protrusion such as a handle or a lid rim.
- Add clearance for whatever protects it: void fill, a fitment, a bag, or a second inner box.
- Write the result as inside dimensions, length x width x depth.
- Add the board thickness from the table above to get the outside dimensions, then check those against your pallet, your shelf and your carrier.
The shipping check most buyers skip
Parcel carriers charge on the greater of actual weight and dimensional weight, which is calculated from the outside dimensions of the box. That means an oversized box charges you twice: once in board you did not need, and again on every parcel for the life of the SKU. Divisors and rules change, so check your carrier's current dimensional weight policy against your outside dimensions before you commit to a die. Half an inch in the wrong direction can move a parcel into a higher band.
Custom sizes, minimums and lead time
Because the die and the plates are included in an iBox Factory order, a size specific to your product costs no more in tooling than a common cube size. The minimum is 100 boxes per size, and pricing starts from about $0.48 per unit at bulk volumes, confirmed on your written quote. Design support, US shipping and a digital proof before anything prints are included as well.
Turnaround is stated per product across three lanes: rush is expedited production plus air freight, standard is air, cost saver is sea. The floor is from about 7 business days plus 2 to 5 for delivery, with specialty imported items running up to about 12 weeks and rush carrying a premium of about 7 to 25% depending on the job.
For the board and flute decision, read custom corrugated boxes. For the measuring method applied to any pack, see how to choose the right box size. When your dimensions are settled, send them through the quote form.
