The number of all the males a month old or more was 7,500.
The Levites being granted to Aaron to minister to him, they are here delivered to him by tale, that he might know what he had, and employ them accordingly. Observe, I. By what rule they were numbered: Every male from a month old and upward, Num 3:15.
Commenting on Numbers 3:14-39
Those that were numbered of them,.... Of the two families that sprung from Gershon: according to the number of all the males, from a month old and upwards: in the said families: even those that were numbered of them, were seven thousand and five hundred; 7,500 men, which was neither the least nor the largest number of the sons of Levi.
Those that were numbered of them, according to the number of all the males, from a month old and upward, [even] those that were numbered of them [were] seven thousand and five hundred. (h) Only numbering the male children.