The Shari’ah not only considers the Islamic monetary standard as a medium of exchange, unit of account, store of value and a standard of deferred payment, but the Islamic functions of money also determine Shari’ah legal injunctions concerning zakat (poor tax), jizya (poll tax), kharaj (tax on conquered territory), diyyat (blood-money), sariqa (theft), mahar (dowry) and sarf (exchange). This study seeks to clarify the weight of the dinar and dirham, since they impart justice as part of Shari’ah law. Through library research and content analysis of literature from the hadith, scholars, mint-masters and writers, different regions had different weights and coin standards, which might imply differing opinions as to what constitutes a legal dinar and dirham. However, narrations have clarified the relationships between the Byzantine dinar and the mithqal of Persia, Makkah, Syria, Egypt and Iraq. Combined with additional numismatic and metrological analysis of surviving coins and glass weights, we discover that each mithqal, dirham, daniq, qirat, habbah and khardal are defined differently, but reflect the same standard of the Prophet (s.a.w.s.) that was later externalized with the minting of the first Islamic dinars and dirhams by Caliph cAbd al-Malik ibn Marwan, involving modern equivalents weights of 4.25g and 2.975g.