Numbers 18:16

And those that are to be redeemed ,.... Which is to be understood not of unclean beasts last mentioned, for they were redeemed with lambs and not with money; and after they were eight days and not a month old, as follows, Exodus 13:13 ; but of the firstborn of men:

from a month old shalt thou redeem, according to thine estimation : that is, take the redemption money next mentioned; and though both time and price are fixed, yet said to be according to the estimation of the priest; see Leviticus 27:5 ,

for the money of five shekels ; which was about eleven or twelve shillings of our money, and is the price given for the redemption of the firstborn, when the Levites were taken in their stead, Numbers 3:47 ,

after the shekel of the sanctuary, which is twenty gerahs ; see Gill on Numbers 3:47 ; of the manner of redeeming the firstborn; see Gill on Exodus 13:15 .