Standards for Weights

The standard Roman weight for dockside trade and bulkier marketplace purchases was the libra. Sets of such weights recovered from Pompeii and Praenaste indicate that 1 libra is equivalent to about 0.71 U.S. pounds [323 grams]. Thereafter, the libra is divided into twelve unciae, so 1 uncium is equivalent to 0.95 U.S ounces [26.9 grams]. Herbalists putting together medicinal concoctions often used this weight, together with its finer fractions that go down to the apothecary's scripulos as a twenty-fourth part of an uncium: thus about 0.039 U.S. ounces [1.12 grams].

Seaborne trade in the Eastern Mediteranean frequently was carried out with the standard weight of the Greek talent which is equivalent to about 57 U.S. pounds [25.9 kilograms]. The hefty talent was broken down into the more domestically relevant units, the mina and the drachma. These, like the libra and the uncium, were used in eastern marketplaces for the sale of produce, medicinal herbs, and culinary spices.

Thus, 1 drachma is equivalent to 0.15 U.S. ounces [4.31 grams].

1 talent = 80 libra
1 mina = 1.33 libra
1 drachma = 0.16 uncium

and

1 talent = 60 minae
1 mina = 100 drachmae
1 drachma = 7 obols