Shipping Glossary

Dimensional Weight

What DIM weight is, how carriers calculate it, and how to avoid overpaying.

Definition

Dimensional weight (DIM weight) is a pricing method used by shipping carriers that calculates a package's billable weight based on its physical dimensions rather than its actual weight on a scale. When the DIM weight exceeds the actual weight, the carrier charges based on the higher DIM weight.

What Is DIM Weight?

DIM weight was introduced because large, lightweight packages take up valuable space in delivery trucks and aircraft. Carriers use a divisor (also called a DIM factor) to convert a package's cubic size into an equivalent weight. FedEx and UPS use a divisor of 139 for domestic shipments, meaning you divide the cubic inches by 139. USPS uses a divisor of 166 and only applies DIM weight to packages over 1 cubic foot. The carrier then compares the DIM weight to the actual weight and charges whichever is higher, a practice known as the 'billable weight' calculation.

Formula

L x W x H (in inches) / DIM divisor = DIM weight (lbs). FedEx/UPS divisor: 139. USPS divisor: 166.

Example

A box measuring 18 x 12 x 8 inches has a volume of 1,728 cubic inches. Using the FedEx/UPS divisor of 139, the DIM weight is 12.4 lbs (rounded up to 13 lbs). If the actual item weighs only 3 lbs, you'll be billed for 13 lbs.

Why It Matters

DIM weight can dramatically increase your shipping costs if you use oversized boxes for lightweight items. Understanding how it works lets you choose the right packaging and avoid paying two to four times more than necessary.

How Each Carrier Handles DIM Weight

USPS

USPS applies DIM weight pricing only to packages exceeding 1 cubic foot (1,728 cubic inches) for Priority Mail and Ground Advantage. The USPS DIM divisor is 166, which is more generous than FedEx or UPS. Packages under 1 cubic foot are charged by actual weight only.

FedEx

FedEx applies DIM weight to all package sizes using a divisor of 139 for domestic shipments and 139 for international. FedEx compares DIM weight to actual weight on every shipment and charges the higher of the two.

UPS

UPS applies DIM weight to all package sizes using a divisor of 139 for domestic and international shipments. Like FedEx, UPS always bills the greater of actual weight or DIM weight with no minimum size threshold.

Tips

Use the smallest box that safely fits your item to minimize DIM weight charges

Consider poly mailers for soft goods -- USPS does not apply DIM pricing to non-rectangular packages

Use I'd Ship That to compare rates across carriers and automatically find the cheapest option based on your package dimensions

If you frequently ship large, light items, USPS is often cheapest due to its higher DIM divisor and 1 cubic foot threshold

Related Terms

Cubic Pricing • Zone-Based Pricing • Flat Rate Shipping

Frequently Asked Questions

How is DIM weight calculated?

Multiply your package's length x width x height in inches, then divide by the carrier's DIM divisor. FedEx and UPS use 139; USPS uses 166. The result is your DIM weight in pounds, rounded up to the next whole number.

Do all carriers use DIM weight?

Yes, USPS, FedEx, and UPS all use DIM weight pricing. However, USPS only applies it to packages over 1 cubic foot, while FedEx and UPS apply it to every package regardless of size.

How can I avoid DIM weight charges?

Use the smallest packaging possible, switch to poly mailers or padded envelopes for non-fragile items, and consider USPS for large lightweight packages since their DIM threshold is more generous. Comparing rates across carriers can also help you find the best price.

What is the difference between DIM weight and actual weight?

Actual weight is what your package weighs on a scale. DIM weight is a calculated weight based on the package's dimensions. Carriers charge whichever is higher. If your package is large but light, DIM weight will likely be higher than actual weight.

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