Grams and troy ounces

Gold Up editorial teamPublished 21 August 2026Updated 21 August 20262 min read

The conversions

Why two kinds of ounce exist

The troy system survived in the precious metals trade long after everyday commerce moved on. It persists because the entire international market — quotes, bar sizes, benchmarks — is built on it. The practical consequence is that a troy ounce is about 10% heavier than the ounce most people picture.

Pennyweights and old scales

Older jewellery scales and some inherited records use pennyweights: twenty to the troy ounce. If you find weights recorded in dwt, multiply by 1.5552 to get grams.

Accuracy matters more than it looks

Trade scales read to a hundredth of a gram and are calibrated. Domestic kitchen scales typically read in whole grams and drift. On a small 22ct item that difference is a meaningful proportion of the gold content, which is why any home estimate should be treated as approximate — see how much is my gold worth.

Weighing a mixed lot

Standards are weighed separately, never together. A pile holding 9ct, 18ct and 22ct has no single gold content: 40 grams of it might contain anywhere between 15 and 36 grams of fine gold depending on how that weight is distributed. Sorting by fineness mark before weighing is what makes any figure meaningful, and it is the first step in a gold valuation.

What the scale reading includes

Stones, clasp springs, watch movements and hollow filling all register on the scale without contributing any gold. On stone-set rings and hollow rope chain the difference is substantial, so a realistic figure comes from the weight of gold rather than the weight of the item.

Grains and older written records

Probate papers and old insurance valuations sometimes record weights in grains: 480 to the troy ounce, so one grain is 0.0648 grams. Bear in mind that a figure written decades ago reflects the gold price of that day, not this one.