Dimensional weight (also called volumetric weight or DIM weight) is how shipping carriers account for the space a package takes up, not just how heavy it is. Carriers charge by whichever is greater: the actual weight of the package or its dimensional weight. This means a large, lightweight box can cost more to ship than you'd expect based on the scale alone.
The formula is: DIM Weight = (Length x Width x Height) / Carrier Divisor. Each carrier uses a different divisor. USPS uses 166 for cubic inches, while UPS, FedEx and DHL use 139. For centimeters, most international carriers use 5000, and Pos Malaysia uses 6000.
The most effective way to avoid DIM weight surcharges is to right-size your packaging. Use the smallest box that safely holds your product with adequate protection. Poly mailers eliminate DIM weight concerns entirely for non-fragile items. If you ship a high volume of the same product, consider custom-sized boxes — even a 1-inch reduction on each side can make a meaningful difference across hundreds of shipments.
Dimensional weight (DIM weight) is a pricing method that reflects how much space a package occupies. Carriers use it because large, lightweight packages take up valuable truck and airplane space. They charge the greater of actual weight or DIM weight to ensure pricing is fair relative to the space used.
Multiply Length x Width x Height (in inches or cm), then divide by the carrier's divisor. For inches: USPS uses 166, UPS/FedEx/DHL use 139. For centimeters: most carriers use 5000, Pos Malaysia uses 6000. Round up to the next whole number. If the result exceeds your actual weight, you'll be billed at the DIM weight.
USPS: 166 (inches) / 5000 (cm). UPS/FedEx/Amazon: 139 (inches) / 5000 (cm). DHL/Royal Mail/Aramex/DPD/Australia Post/Canada Post/SingPost: 5000 (cm). Pos Malaysia/J&T/Ninja Van/SPX/Flash Express: 6000 (cm). A lower divisor means higher DIM weight.
Right-size your packaging to fit the product snugly. Use poly mailers instead of boxes for soft goods. Consider USPS Priority Mail Flat Rate boxes which aren't subject to DIM pricing. For high-volume shippers, custom-sized boxes can save significantly. Even reducing each dimension by 1-2 inches can make a big difference.
No. USPS only applies DIM weight pricing to Priority Mail packages exceeding 1 cubic foot (1,728 cubic inches). Smaller packages are charged by actual weight. Priority Mail Flat Rate boxes, First-Class Mail, and Media Mail are not subject to DIM weight pricing at all.