How to Measure a Corrugated Box Correctly
A box size is written as Length x Width x Height, in that order. Length is the longer side of the opening, width the shorter side, and height runs from the opening down to the base. Manufacturers work from internal dimensions, because that is the space your product actually gets.
Internal vs external size
Internal size is the usable space inside the box. External size is what the box occupies in a courier bag, a shelf or a container. Board thickness sits between the two, so a 5 ply box loses more internal space than a 3 ply box at the same external size. When you order, quote internal dimensions and say so. A box ordered by external size often turns up tight.
The measuring routine
- Open the box flat is not needed. Measure across the opening: longer side first, that is Length.
- Measure the shorter side of the opening: Width.
- Measure from the opening to the base: Height.
- Measure in millimetres where possible. Inches work too, just never mix units in one order.
Terms you will see on a spec
| Term | Meaning |
|---|---|
| L x W x H | Length, width, height of the opening and depth |
| ID / OD | Internal dimension / outer dimension |
| Tolerance | Small allowed variation in manufacturing, a few millimetres |
| Knocked down | Box supplied flat, folded and glued or stitched at one joint |
If the product is fragile or oddly shaped, add the cushioning to your internal size before ordering. A snug box protects better than a loose one, but a box with no allowance at all fights you at the packing table.
Frequently asked questions
Which side is length if both look equal?
If the opening is square, either side can be length. Just keep the order consistent on the spec.
Should I order by internal or external size?
Internal, unless a courier or shelf limit forces an external cap. Tell the unit which one you mean.
How much bigger than my product should the box be?
Enough for your cushioning and easy packing. For most products a small, deliberate allowance beats a loose fit.