“A shekel is twenty gerahs.” That is nearly all the Bible says about the gerah, and it says it three times, always alongside “the shekel of the sanctuary,” the standard used for what was given to the LORD. In Exodus 30 each person who was numbered gave half a shekel as an offering. Leviticus 27 uses it for valuing things that had been set apart, and Numbers 3 uses it for a payment of five shekels a head. The gerah is small change, but it shows how carefully the Law spelled out what a gift should weigh.
3 verses
This they shall give, every one that passeth among them that are numbered, half a shekel after the shekel of the sanctuary:(a shekel is twenty gerahs:) an half shekel shall be the offering of the LORD.
And all thy estimations shall be according to the shekel of the sanctuary: twenty gerahs shall be the shekel.
Thou shalt even take five shekels apiece by the poll, after the shekel of the sanctuary shalt thou take them:(the shekel is twenty gerahs:)
Matthew George Easton, 1897
A bean, probably of the carob tree, the smallest weight, and also the smallest piece of money, among the Hebrews, equal to the twentieth part of a shekel (Ex. 30:13; Lev. 27:25; Num. 3:47). This word came into use in the same way as our word “grain,” from a grain of wheat.
William Smith, 1884
[WEIGHTS AND MEASURES AND MEASURES]