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,

Numbers 3:47; of the manner of redeeming the firstborn,

Exodus 13:15.