Numbers 18:16
And those that are to be redeemed from a month old shalt thou redeem, according to thine estimation, for the money of five shekels, after the shekel of the sanctuary, which is twenty gerahs.
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".