It was originally a fifth of a denarius or zuz, as seen in the Torah and in Ezekiel (45:12), then became a sixth of a dinar/zuz, such as the coinage of Persian-era Yehud, which came in two denominations: approximately 0.58 gram for the ma'ah and approximately .29 gram for the half ma'ah (chatzi ma'ah).
Originally a fifth of a denarius or zuz, as seen in the Torah and in Ezekiel (45:12), it later became a sixth of a dinar/zuz, such as the coinage of Persian-era Yehud, which had two denominations: approximately 0.58 grams for the ma'ah and approximately .29 grams for the half ma'ah (chatzi ma'ah).