What is dimensional weight?
Dimensional weight (DIM weight, or volumetric weight) is how carriers price light but bulky packages. A big box of sweaters takes up as much room in a truck as a box of books, so carriers charge for whichever is greater: the actual weight or the dimensional weight. The greater of the two is the billable weight.
How to calculate dimensional weight
- Measure the box in inches: length, width and height. Round each side to the nearest inch.
- Multiply them to get the volume in cubic inches.
- Divide by the carrier's divisor: 139 for UPS and FedEx, 166 for USPS.
- Round up to the next whole pound. Compare with the actual weight (also rounded up); the larger one is what you pay for.
Example: a 14 × 10 × 6 in box is 840 cubic inches. With UPS, 840 ÷ 139 = 6.04, so it bills as 7 lb even if it weighs 2 lb. USPS doesn't apply DIM weight to boxes under one cubic foot (1,728 cu in), so the same box bills at its actual 2 lb.
How to avoid paying for air
- Use the smallest box that fits. Every inch counts because all three sides are multiplied.
- Use poly mailers for clothing. Soft items in a mailer have tiny dimensions and usually bill by actual weight.
- Stay under one cubic foot with USPS (for example 12 × 12 × 12 in or smaller) so you only pay for actual weight.
- Check flat-rate options. For heavy, dense items, USPS Priority Mail flat-rate boxes can beat weight-based pricing.
FAQ
Does USPS charge dimensional weight?
Yes, for Priority Mail and Ground Advantage packages larger than one cubic foot (1,728 cubic inches). Smaller packages are charged by actual weight.
What divisor do UPS and FedEx use?
139 for standard daily and retail rates in the US. Some business accounts negotiate a higher divisor, which lowers DIM weight.
How do I calculate dimensional weight in centimeters?
Switch the units to centimeters and kilograms above. The calculator converts to inches the way US carriers bill, and shows the results in kilograms.
Do Vinted, eBay or Poshmark labels use dimensional weight?
Prepaid labels from marketplaces usually price by weight tier for small packages. The carrier can still adjust the charge for large boxes, so a compact package is always the safe choice.