What is "DIM Weight"?

Dimensional Weight (DIM Weight) determines a package’s density rather than just its weight and reflects the amount of space the package will occupy in transit, compared to its physical weight. Actual weight pricing is purely based on how many pounds the package weighs.

For each shipment, carriers charge based on the dim weight or the actual weight, whichever is greater.

Note: The units are inches.

Calculating Dimensional Weight

DIM Weight is calculated by:

Length x Width x Height of parcel*/DIMfactor

Carriers set their own DIM Factors.
Higher DIM factors mean the calculated DIM Weight will be lower and therefore be applied less often.
Some carriers only charge DIM Weight packages over 1 cubic foot or 1728 cubic inches.

USPS: LxWxH/166
FedEx Ground (Includes Services Ground, Home Delivery, not including SmartPost): LxWxH/225
FedEx Express (Includes 2Day, 2Day AM, Express Saver, Priority Overnight, and Standard Overnight): LxWxH/225
FedEx SmartPost: LxWxH/139
UPS (All Services Except for SurePost): LxWxH/250
UPS SurePost: LxWxH/139
DHL: LxWxH/166

Domestic shipments under 1 cubic foot = 1728 cubic inches and/or under 1 pound are not subject
to Chargeable Weight rules and are invoiced based on the actual weight.

Dimensional Restrictions

Some methods prohibit parcels over a certain size or apply surcharges. Information about DHL's dimensional restrictions can be found here: DHL SmartMail Parcel

Example

I have a package with 2 lbs. of actual weight in a 16 x 8 x 10" box.

Each carrier would rate the package as though it were 6–12lbs: