What Is Dimensional Weight?
Dimensional weight (also called DIM weight, volumetric weight, or cubed weight) is a pricing technique used by UPS, FedEx, and other carriers to account for the space a package occupies in their vehicles and aircraft. When a package is light but bulky, dimensional weight may exceed the package’s actual weight, and carriers bill at the higher of the two.
DIM pricing was introduced to address the economics of shipping: a carrier’s vehicle fills up with volume long before it reaches its weight capacity when handling large, lightweight packages. DIM weight pricing ensures shippers pay for the space their packages occupy, not just the pounds they weigh.
The DIM Weight Formula (UPS & FedEx)
The standard DIM weight formula is:
DIM Weight = (Length x Width x Height) / DIM Divisor
All measurements are in inches, and the result is in pounds. The DIM divisor (also called the DIM factor) is set by each carrier and service level:
- UPS and FedEx Ground: 139 (as of 2024)
- UPS and FedEx Express (air services): 139
- USPS Priority Mail: 166
Example: A box measuring 18″ x 14″ x 12″ has a volume of 3,024 cubic inches. Divided by 139, the DIM weight is 21.8 lbs, rounded up to 22 lbs. If the actual weight is 8 lbs, the carrier bills at 22 lbs (the DIM weight).
The DIM divisor has changed over time. UPS and FedEx reduced it from 166 to 139 in 2015, which effectively raised DIM charges across the industry. A lower DIM divisor means more packages trigger DIM billing.
Actual Weight vs. Billable Weight vs. Dimensional Weight
These three weight terms are frequently confused. Here is the precise distinction:
- Actual weight: The physical weight of the package on a scale, rounded up to the nearest pound. Sometimes called scale weight.
- Dimensional weight: The calculated weight based on the package’s cubic volume divided by the DIM divisor. Represents the space the package occupies rather than its true mass.
- Billable weight: The weight the carrier actually uses to calculate your shipping charge. It is always the greater of actual weight and dimensional weight. If your DIM weight is higher than your actual weight, you pay the DIM weight.
When carriers refer to Billed Weight on an invoice, they mean billable weight after comparing actual vs. DIM and choosing the larger figure.
How Package Dimensions (L × W × H) Affect Your Bill
Measuring packages consistently matters for DIM calculations and carrier compliance. Carriers define these dimensions as:
- Length: The longest side of the package
- Width: The second-longest side
- Height: The shortest dimension (vertical when the package is resting on its base)
All three measurements are taken at the longest point of each dimension. Rounded corners or irregular shapes are measured at their maximum extent. For non-rectangular packages, carriers measure the dimensions of the smallest rectangular box that would fully contain the shipment.
What Is Girth and Why Does It Matter?
Girth is the measurement around the thickest part of a package, perpendicular to its length. The formula is:
Girth = 2 x (Width + Height)
Girth is used alongside length in the “length plus girth” measurement that determines whether a package qualifies as a Large Package. Both UPS and FedEx define a Large Package as one where length + girth exceeds 130 inches. Large packages trigger a Large Package Surcharge (approximately $57 to $90+ per package).
Example: A package 50″ long with a 14″ x 14″ cross-section has a girth of 2 x (14 + 14) = 56″. Length + girth = 50 + 56 = 106″ — below the 130″ threshold, so no Large Package Surcharge applies.
Gross Weight vs. Net Weight
- Gross weight: The total weight of a shipment including the product, all packaging materials, and the shipping container. This is what carriers use for billing.
- Net weight: The weight of the product only, excluding packaging. Required on customs declarations and commercial invoices for international shipments.
Density and Its Role in Freight Classification
Density is a key factor in LTL (Less Than Truckload) freight pricing. It is calculated as:
Density = Weight (lbs) / Volume (cubic feet)
In LTL shipping, density determines a shipment’s freight class (NMFC class), which sets the applicable tariff rate. Higher-density freight generally falls into lower freight classes with lower rates. Lower-density freight falls into higher freight classes with higher rates. For parcel shippers, low-density packages are the primary trigger for dimensional weight billing.
How to Reduce Dimensional Weight Charges
Dimensional weight is largely within shippers’ control. The most effective strategies include:
- Right-size your packaging: Match box size as closely as possible to product size. Every inch of excess box dimension increases DIM weight. Many shippers maintain too few box sizes — adding intermediate sizes can eliminate DIM overcharges on a large portion of shipments.
- Negotiate your DIM divisor: The DIM divisor (139 for UPS/FedEx) is negotiable for large-volume shippers. Even a small increase from 139 to 155 translates to meaningful savings across high-volume accounts.
- Audit for DIM billing errors: Carriers occasionally mis-measure packages. A systematic audit of DIM charges against your actual package dimensions can recover refunds for incorrect measurements.
- Use poly mailers for soft goods: Poly mailers conform to the product shape, minimizing void space and DIM weight for eligible product types (apparel, soft goods).
Shipware’s contract optimization team has helped hundreds of shippers reduce DIM weight costs through package audits, divisor negotiation, and carrier contract restructuring. Request a free shipping cost analysis to identify exactly where you’re overpaying on dimensional weight charges. Also explore our shipping optimization services or return to the full shipping glossary.