The DIM weight is the volume of a package it occupies in a truck or warehouse shelf.
FedEx dimensional (DIM) weight is a pricing method used by FedEx to charge for shipping based on package size and the space it occupies, rather than just its actual weight.
FedEx calculates both the actual weight and the DIM weight of your package, then bills you for whichever is greater. If your box is large but lightweight, you may pay based on its dimensional weight instead of its actual scale weight.
FedEx DIM Weight Formula
To find the DIM weight, you multiply the package’s dimensions and divide by a specific “divisor” set by FedEx.
DIM weight (lbs) = (Length × Width × Height in inches) / 139
- Measurements are in inches.
- Standard divisor: 139 (standard for FedEx Express, Ground, and Home Delivery).
- Rounding rule: As of August 2025, FedEx rounds every fraction of an inch up to the next whole inch before calculating. For example, a box that is 10.1″ wide is treated as 11″. The final DIM weight result is rounded up to the nearest whole pound.
FedEx charges whichever is greater:
- Actual weight
- Dimensional weight
Example:
If your box measures 20″ × 16″ × 12″
Calculation:
20 × 16 × 12 = 3,840 cubic inches
3,840 ÷ 139 = 27.6
Rounded up: 28 lbs DIM weight
If the actual weight is 22 lbs, you’ll be charged for 28 lbs.
Why FedEx uses DIM weight?
- Prevents shippers from using oversized packaging unnecessarily.
- Encourages efficient packing to reduce shipping costs.
- Optimizes cargo space in planes and trucks.
- Helps them to price shipments more fairly based on space used.