Exodus 30:11-16 (NKJV)
¹¹  Then the LORD spoke to Moses, saying:
¹²  “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.
¹³  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.
¹⁴  Everyone included among those who are numbered, from twenty years old and above, shall give an offering to the LORD.
¹⁵  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.
¹⁶  And you shall take the atonement money of the children of Israel, and shall appoint it for the service of the tabernacle of meeting, that it may be a memorial for the children of Israel before the LORD, to make atonement for yourselves.”