Dimensional weight, also called volumetric weight or DIM weight, is how carriers charge for the space a parcel occupies rather than what it weighs. A vehicle fills up before it weighs out, so light bulky freight is priced on volume. If you sell anything light in a generous box, this is probably the largest hidden cost in your packaging.
The arithmetic
Take the outside dimensions of the packed box in inches, which is what the carrier measures, not the internal dimension you specified. Multiply them together for cubic inches. Divide by the carrier's divisor. Round up to the next whole pound. Compare that figure with the actual scale weight. The higher of the two is your billable weight.
| Box (outside, in) | Cubic inches | At a 139 divisor | Billable if it weighs 4 lb |
|---|---|---|---|
| 12 x 12 x 12 | 1,728 | 12.4, rounds to 13 | 13 lb |
| 10 x 10 x 10 | 1,000 | 7.2, rounds to 8 | 8 lb |
| 14 x 10 x 6 | 840 | 6.0, rounds to 6 | 6 lb |
| 9 x 7 x 4 | 252 | 1.8, rounds to 2 | 4 lb, actual weight wins |
That last row is the point where dimensional weight stops mattering: once the box is tight enough, the scale weight is higher and you are billed on that instead.
Which divisor applies
Divisors are published by each carrier and they change. US domestic parcel services commonly use 139 cubic inches per pound; 166 shows up on some services and rate types, and international air services use their own. A larger divisor is better for you, because it converts the same volume into fewer pounds. Do not take a number from a blog, including this one, as current. Look it up on the rate card you are actually billed against, then run your own boxes through it.
How to actually reduce it
- Cut the empty space. This is the whole answer. Measure the packed load, add only the cushion you need, and specify that internal dimension. Because the die is included in a custom run, a box cut to your exact load costs no more to tool than an off-the-shelf size that is two inches too big in every direction.
- Attack the largest dimension first. Volume is a product of three numbers, so an inch off the biggest one removes more cubic inches than an inch off the smallest.
- Use more than one box size. A single box sized for your largest order overcharges you on every small one. Two or three sizes across your order profile usually pays for itself quickly.
- Consider a mailer instead of a box for soft goods, since a flat pack has a far smaller cubic volume than a rigid box holding the same item.
- Check rounding. Carriers round dimensions up to the next whole inch before the calculation, so a box that measures 12.1 inches is measured as 13. Board caliper and a bulging side panel both push you over a boundary.
What this means when you order packaging
Dimensional weight is a recurring cost and packaging is a one-time cost, so it is usually worth spending slightly more on a box that fits than saving on one that does not. The minimum here is 100 boxes and pricing starts from about $0.48 per unit at bulk volumes, confirmed on your written quote, with the die, the plates, design support, US shipping and a digital proof before printing included. We make in West Chicago in the US and Guangzhou in China, and turnaround is quoted per product in three lanes: rush (expedited production plus air freight), standard (air) and cost saver (sea), from about 7 business days plus 2 to 5 for delivery.
The method for getting the size right is on how to size a corrugated shipping box, and if soft goods are the problem, compare against poly mailer dimensions.
If you tell us your current box size and what goes in it on the quote form, we will quote the tighter size alongside it so you can compare the packaging cost against the shipping cost with real numbers.
