The smallest weight: a twentieth of a shekel, about half a gram.
Mass
0.55–0.575 g (0.0194–0.0203 oz).
Defined as 1/20 of a shekel.
A gerah is a grain or a seed, and at about half a gram it is the finest weight scripture names. It exists in the text mainly to define the shekel — twenty gerahs make one — and to fix the redemption prices in Leviticus, where small sums had to be exact.
Silver was weighed, not counted, until coins reached Judah, so each weight is drawn as the cube that much silver makes. A shekel is about a centimetre across; the thirty pieces of silver would sit in a palm; a talent is a block a hand and a half wide.