It is implied that Ezekiel is comparing the prince's land with the size of the land given to each of the tribes. Alternate translation: "The length will be the same as the length of one of the portions given to the tribes" (See: [[rc://en/ta/man/translate/figs-explicit]])
It is implied that these are the western and eastern borders of the land of Israel. "from the western border of Israel at the sea to the eastern border at the Jordan River"