usps ground advantage cubic meaning is a term used to describe USPS’s Ground Advantage service, which is based on the cubic measurement of a package. USPS offers Ground Advantage as an affordable shipping option for packages weighing up to 70 pounds and measuring up to 108 inches in combined length and girth. The cubic measurement refers to the volume of the package, and rates may vary based on the package’s size and weight. The Ground Advantage service offers delivery within 1-5 business days.