Choosing a box size is a five step calculation, and skipping any one of them is what produces boxes that arrive and do not fit. Here is the method, in the order to do it.
Step 1: measure the product at its worst
Measure the largest example you have, in its packed state, at the widest point in each direction. Include anything that sticks out: a pump head, a handle, a lid rim, a hinge, a crimped tube tail. If your product varies (glass, ceramic, anything moulded or hand made), measure several and use the biggest. Sizing to an average guarantees that some percentage of your run will not fit.
Step 2: add clearance for what surrounds it
Clearance is not a fixed allowance, it is the thickness of whatever sits between the product and the wall.
| What goes around the product | What it adds |
|---|---|
| Nothing, snug fit | A small allowance so the product can be inserted at speed |
| A bag, wrap or tissue | The material thickness, doubled where it folds |
| A corrugated or chipboard fitment | The board caliper on every side it touches |
| Foam or moulded pulp | The cushion thickness you have specified on each face |
| Loose void fill | Enough space for the fill to actually cushion, not just occupy |
Step 3: write it as inside dimensions
Length is the longer of the two edges at the opening, width the shorter, depth the distance from opening to base. Put those three numbers in that order and label them as inside dimensions. Ninety percent of sizing confusion between a buyer and a supplier is one party quoting outside dimensions while the other reads them as inside.
Step 4: convert to outside dimensions
Add the board thickness on both walls of each dimension. On a single wall C flute corrugated box that is roughly 3/8 inch added to each dimension. On a thin folding carton it is negligible. The full table is on corrugated box dimensions. Outside dimensions are what your pallet, your shelf and your carrier care about.
Step 5: check the shipping maths before you commit
Parcel carriers charge on the greater of actual weight and dimensional weight, and dimensional weight is calculated from outside dimensions. Check your outside dimensions against your carrier's current rules before the die is cut, because half an inch can move a parcel into a more expensive band and you will pay that on every order for years. Also check how the box sits on a pallet: a size that leaves a large gap in each pallet layer is quietly expensive on freight.
Three sizing mistakes worth avoiding
- Sizing to a prototype rather than to production stock. The final product is rarely identical to the sample.
- Designing one box to fit everything. A box that fits your largest item wastes space on the smallest, and void fill is not free.
- Assuming a custom size costs more. The die and the plates are included, so the tooling for a size that suits your product is the same as for a common cube.
Getting it made
Minimum 100 boxes per size. Pricing starts from about $0.48 per unit at bulk volumes and is confirmed on your written quote, and the die, the plates, design support, US shipping and a digital proof are included. Turnaround is stated per product across three lanes: rush is expedited production plus air freight, standard is air, and cost saver is sea, from about 7 business days plus 2 to 5 for delivery, with specialty imported items up to about 12 weeks.
If you would rather we did the maths, send the product dimensions and what goes around it through the quote form and we will come back with inside and outside dimensions on a dieline. To sanity check the budget first, read how much custom boxes cost.
