How to calculate dimensional weight.

The formula

Multiply length × width × height in inches, then divide by your carrier's DIM divisor. Round the result up to the next whole pound. That is your dimensional weight.

A worked example

A 20 × 16 × 12 inch box is 3,840 cubic inches. Divided by a 139 divisor, that is 27.6, which rounds up to 28 lbs of dimensional weight. If the box actually weighs 6 lbs, you are billed on 28.

Which weight you pay

You always pay on the greater of actual weight and dimensional weight, then on the destination zone. So light, bulky packages are almost always billed on DIM.