Exodus 30:11-15

Then the LORD spoke to Moses, saying: “When you take the census of the children of Israel for their number, then every man shall give a ransom for himself to the LORD, when you number them, that there may be no plague among them when you number them. This is what everyone among those who are numbered shall give: half a shekel according to the shekel of the sanctuary (a shekel is twenty gerahs). The half-shekel shall be an offering to the LORD. Everyone included among those who are numbered, from twenty years old and above, shall give an offering to the LORD. The rich shall not give more and the poor shall not give less than half a shekel, when you give an offering to the LORD, to make atonement for yourselves.