Dim weight is not the same across USPS, UPS and FedEx. Quick reference after the July USPS change

Posted by u/One_Gur_7504

USPS dropped its dimensional weight divisor from 166 to 139 on 12 July 2026, but it still only applies to boxes over 1 cubic foot (1,728 cu in). Under that, you pay actual weight.

UPS uses 139 on daily rates and 166 on retail. FedEx uses 139. UPS and USPS round each side up to the next inch; FedEx rounds to the nearest inch. All three round the result up to the next pound and bill whichever is higher, dim or actual.

Example: 16x12x8 box, 4 lb actual. USPS bills 4 lb (under 1 cu ft). UPS daily and FedEx bill 12 lb. UPS retail bills 10 lb.

If you ship light, bulky items, dropping one box size often saves more than switching carriers. Happy to sanity-check anyone’s box sizes.