Dimensional Weight
Definition
A pricing method where carriers charge based on a package's size instead of its actual weight when the package is large and light.
Want a deeper explanation?
Formula
Dimensional Weight (lb) = (Length × Width × Height in inches) ÷ Carrier Divisor (often 139)Dim weight is why packaging design is a finance decision. Shaving two inches off a box can cut shipping cost more than any carrier discount.
Amazon applies similar logic to FBA fees through size tiers. Watch for: rising average shipping cost per order with no change in product mix, which often means packaging crept bigger.
Example
A 20 × 16 × 12 inch box weighing 6 lb has a dimensional weight of about 28 lb (3,840 ÷ 139), so you are billed for 28 lb, not 6.