Dimensional Weight
Also known as: DIM Weight, Volumetric Weight
Dimensional weight is a pricing weight derived from a package's volume (length × width × height ÷ a divisor) used when a bulky-but-light item would otherwise be underpriced by actual weight.
Dimensional (DIM) weight prices the space a package occupies rather than just its mass, so a large, light item is not shipped for the same fee as a small, dense one. The formula is DIM weight = (L × W × H) / dimensional divisor, with dimensions in inches.
Amazon FBA fulfillment fees use "shipping weight," which is the GREATER of the unit's actual unit weight and its dimensional weight. For most FBA standard and large/bulky size tiers Amazon uses a divisor of 139 (cubic inches per pound). A pillow, for example, weighs little but bills on its bulk.
Understanding DIM weight matters when choosing packaging and product dimensions: shrinking a box just under a size-tier or weight-band boundary can drop the fulfillment fee meaningfully, and packing efficiently lowers the dimensional weight that drives the fee.
A box is 18 × 12 × 10 inches = 2,160 cubic inches. DIM weight = 2,160 / 139 ≈ 15.5 lb. If the item actually weighs 6 lb, the FBA fee is billed on the 15.5 lb dimensional weight, not the 6 lb actual weight.