Troy Ounces vs. Regular Avoirdupois Ounces: Bullion & Jewelry Weight Guide

In everyday commerce, postal shipping, and grocery measurements, the United States and Commonwealth use the Avoirdupois system, where 1 ounce equals 437.5 grains (exactly 28.349523125 grams). However, precious metals—including gold, silver, platinum, palladium, and bullion coins—are exclusively weighed and priced in the Troy system, originating from the medieval trade fairs of Troyes, France. One Troy ounce (oz t) is legally defined as 480 grains, or exactly 31.1034768 grams.

Because 1 Troy ounce (31.1035 g) is heavier than 1 Avoirdupois ounce (28.3495 g), many people assume a Troy pound is also heavier than a regular pound. In fact, the opposite is true: a regular Avoirdupois pound is divided into 16 ounces (7,000 grains = 453.59237 g), whereas a historical Troy pound was divided into only 12 Troy ounces (5,760 grains = 373.2417 g). To avoid confusion, modern bullion markets quote large bars exclusively in Troy ounces (e.g., 100 oz t or 400 oz t Good Delivery bars) or metric kilograms.

• 1 Troy Ounce (oz t) = 20 Pennyweights (dwt) = 480 Grains = 31.1034768 Grams • 1 Pennyweight (dwt) = 24 Grains = 1.55517384 Grams (used by jewelers for ring shanks and dental alloys) • 1 Metric Carat (ct) = 0.2 Grams = 200 Milligrams (used for diamonds and gemstones; distinct from 'karat' gold purity where 24K = 99.9% pure gold).