Dimensional weight, explained.

What dimensional weight is

Carriers have limited space on a truck or plane, so they charge for volume as well as weight. Dimensional weight converts a package's size into a billable weight. You pay on whichever is higher: the package's actual weight or its dimensional weight.

For dense items, actual weight usually wins. For light, bulky items (think a pillow or an empty-ish box), dimensional weight wins, and it can be several times the real weight.

How to calculate it

Multiply length × width × height in inches, then divide by the carrier's DIM divisor. A 20 × 16 × 12 inch box is 3,840 cubic inches. At a divisor of 139, that is about 28 lbs of dimensional weight, even if the box weighs 6 lbs. You would be billed on 28 lbs.

What the divisor means

The divisor is the lever. A lower divisor produces a higher dimensional weight and a higher bill. Carriers have shifted divisors lower over time, which quietly raises costs. The divisor is also negotiable in a carrier agreement, which is why it is a frequent target in a rate negotiation.

How to reduce dimensional weight charges

• Right-size your packaging so boxes match their contents.
• Negotiate the DIM divisor and minimums in your carrier agreement.
• Audit invoices for misapplied or miscalculated DIM charges.
• Reconsider carrier or service mix for bulky lanes.