Exodus 30:13-15

13Everyone among them who crosses over must give half a shekel according to the Sanctuary shekel (which is 20 gerahs): half a shekel as an offering to Adonai.

14Everyone who crosses over among them who is counted, from 20 years old and upward, is to give the offering to Adonai.

15The rich are not to give more and the poor are not to give less than the half shekel, when they present the offering of Adonai to make atonement for your souls.