How this calculator works
Dimensional (DIM) weight is the box volume divided by a divisor. In inches and pounds, UPS and FedEx divide cubic inches by 139. The carrier then bills whichever is higher, the actual weight or the dimensional weight.
Each dimension is rounded up to the next whole inch before multiplying, and the result is rounded up to the next whole pound. A box measuring 17.2 inches is billed as 18.
USPS changed its rules on July 12, 2026: the divisor fell from 166 to 139, the same as UPS and FedEx, and dimensions now round up to the next whole inch. USPS still applies dimensional weight only to parcels larger than one cubic foot (1,728 cubic inches). The calculator shows the old figure too, so you can see what changed.
For shipments measured in centimetres and kilograms, express carriers divide cubic centimetres by 5,000 and bill in half-kilogram steps. Some airlines and freight forwarders use 6,000; enter it as a custom divisor.
Retail counter rates, negotiated contracts and freight services can use other divisors. If your account uses one, the custom field applies it.
Worked example
An 18 × 14 × 10 inch box weighing 6 pounds
- Volume: 18 × 14 × 10 = 2,520 cubic inches.
- UPS and FedEx: 2,520 ÷ 139 = 18.1, rounded up to 19 lb. Billable weight: 19 lb, not 6.
- USPS since July 12, 2026: also 19 lb. Before the change it was 2,520 ÷ 166 = 15.2, so 16 lb.
- A 16 × 12 × 8 inch box (1,536 cubic inches) would bill at 12 lb at UPS and FedEx, and at its actual 6 lb at USPS, which ignores DIM weight below one cubic foot.
Questions people ask
What is the dimensional weight divisor for 2026?
139 for UPS, FedEx and, since July 12, 2026, USPS, with dimensions in inches and weight in pounds. For centimetres and kilograms, international express shipments generally use 5,000.
Does USPS charge dimensional weight on small boxes?
No. USPS applies dimensional weight only to parcels over one cubic foot (1,728 cubic inches). Smaller parcels are charged on actual weight.
How can I lower my dimensional weight?
Use the smallest box that protects the item. Taking an inch off each side of an 18 × 14 × 10 box (to 17 × 13 × 9) cuts its billable weight at a 139 divisor from 19 lb to 15 lb.
Is dimensional weight the same for freight?
No. Pallet freight uses density and freight class, air cargo commonly uses 6,000 cm³ per kg, and sea freight bills by cubic metre. Use the CBM calculator for larger shipments.
Sources
Last reviewed October 2, 2026