Carriers charge shipping on whichever is bigger: actual weight or dimensional weight. A 2-pound box that takes up a shoebox of space gets billed like the shoebox, not the 2 pounds. That's the whole rule.
To calculate dimensional weight, multiply length × width × height in inches, divide by your carrier's dim factor (166 for UPS Ground; FedEx and USPS use 139 or 166 depending on service tier), and round up. Compare that to actual weight: the bigger number is the billable weight.
How Dimensional Weight Impacts Shipping Costs
When shipping goods, the cost is determined by two factors: the actual weight and the dimensional weight. For small, lightweight packages that take up a lot of space, dimensional weight charges are higher than for packages with greater actual weights.
To calculate dimensional weight:
- Measure the length, width, and height of the package in inches
- Multiply the dimensions together to get the cubic size
- Divide the cubic size by the carrier's dimensional factor (such as 166 for UPS)
- Round up to the next whole number
This dim weight is used, along with the actual weight, to calculate shipping costs. Generally, if the dimensional weight is higher than the actual weight, you'll pay shipping based on the dimensional weight.
Why Dimensional Weight Matters
Dimensional weight helps carriers account for packages that take up more space relative to their actual weight. Without it, light but bulky packages would be undercharged compared to dense packages with the same dimensions. It encourages efficient packaging that maximizes space.
Knowing both weights for your packages helps minimize shipping costs. You can optimize package size and shape to avoid dimensional weight charges when possible.
Tips for Lower Dimensional Weight
- Drop a box size when the product fits: every inch off L × W × H drops the bill
- Cut air pockets: use rigid mailers for flat items instead of boxed-with-fill
- Consolidate multi-item orders: two small boxes usually cost more than one slightly bigger one
While dimensional weight adds complexity, understanding how it works helps get the best shipping rates.
Use our dimensional weight calculator to optimize packaging.
Dimensional weight is the lever, not the rule. Most reboxes that cut a quarter-inch off a side change which weight wins (and which rate you pay). The dim-weight calculator runs the math against the major carriers.
Recommended: Cheapest Way to Ship Large or Oversized Packages