A gerah (Hebrew: גרה, romanized: gêrāh) is an ancient Hebrew unit of weight and currency, which, according to the Book of Exodus (30:13), was equivalent to 1⁄20 of a shekel. God tells Moses, the payment for life ransom during the census taking is half a shekel, "which weighs ten gerah". This would make a whole shekel equal to 20 gerah.
A gerah is in Aramaic a ma'ah (מעה; Mishnah Hebrew pl. ma'ot "מעות" which means "coins"). It was originally a fifth of a denarius or zuz, as seen in Exodus ("20 gerah is a shekel"), then became a sixth of a denar/zuz, such as the Yehud coins which came in two denominations, approximately 0.58 gram as a ma'ah and approximately .29 gram as a half ma'ah (chatzi ma'ah), and (.58 X 6 = 3.48) which is about the weight of a Zuz/Denarius based on a 14 gram Shekel.