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The weights of Roman commerce, from the scrupulum to the libra. Part of the Ancient Measures collection.
Every unit converts through grams: libra = 327.45 g, uncia = libra/12, scrupulum = uncia/24. Worked example: a Roman soldier’s annual pay in Augustus’s time, 225 denarii at ~3.9 g each ≈ 878 g of silver = 2.68 librae. The libra’s exact value is reconstructed from thousands of surviving bronze weights; 327–328 g is the consensus range.
About 327 g (11.5 oz) — roughly three-quarters of a modern pound. That is why the abbreviation ‘lb’ (libra) survives on every Anglo-Saxon scale.
1/24 of an uncia, about 1.14 g — a ‘small sharp stone.’ It weighed medicines and precious metals, and gave English the word ‘scruple’: a tiny weight on the conscience.
From uncia, one-twelfth — the Roman twelfth of a libra. The avoirdupois ounce (28.35 g) is close to the Roman uncia (27.3 g).
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