Understanding Dimensional Weight: Why Do Lightweight Packages Cost So Much To Ship Sometimes?

Every online seller has experienced taking a lightweight package to the local USPS or Fedex store only to find out it costs way more to ship the package than they originally thought. This occurs due to something known as dimensional weight (dim weight).

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What is Dimensional Weight?

Dimensional weight is a pricing technique used by many carriers in both the freight and parcel industry. By using the volume of a box or package, the carrier is able to estimate the weight of the package. This estimate can be used in place of the actual weight of a package if it is greater than the actual weight. This allows the carrier to charge for both the space and the weight in their trailer, plane, or shipping container.

How Do I Calculate Dimensional Weight?

Another name for dimensional weight is volumetric weight. This is because you are charged based on the volume of the package. To calculate the volume of a box you would use the formula Volume = Length x Width x Height or simply V = L x W x H. To get to dimensional weight you then divide your package’s volume by what is known by a dimensional factor (DIM factor). This will give you your dimensional weight in pounds (lbs).

What Is A Dimensional Factor?

A DIM factor is simply a value set by a carrier to represent the volume of a package that is allowed for each unit of mass. For example, if a DIM factor is 100 then for every 100 cubic inches of volume you would be allowed up to 1lb of shipping weight before being billed at actual weight.

What Are The Current DIM Factors Of Major Carriers?

FEDEX: 139

UPS: 139

USPS: 166 (Only packages over 1 cubic ft)

Could You Give Me Some Practical Examples?

Example A:

Package Dimensions: 12 x 12 x 6

Actual Weight: 4 lbs

Carrier: UPS

V = L x W x H

V = 12 x 12 x 6


DIM Weight = Volume / DIM Factor

DW = 864 / 139 = 6.22 lb = 7lb

7lb > 4lb

This package would bill at the 7 lb rate as the DIM weight is greater than the actual weight.

Example B:

Package Dimensions: 6 x 6 x 4

Weight: 3 lbs

Carrier: FEDEX

V = L x W x H

V = 6 x 6 x 4


DIM Weight = Volume / DIM Factor

DW = 144 / 139 = 1.03 lb = 2lb

2lb < 3lb

This package would bill at the 3 lb rate as the actual weight is greater than the DIM weight.

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