Troy Ounces to Grams Converter

What this converter does

It converts troy ounces to grams by multiplying by exactly 31.1034768. The troy ounce is the unit gold, silver, platinum and palladium are priced in worldwide, and it is emphatically not the ounce on a kitchen scale. The nearly ten percent difference between the two is the reason this page exists as a separate converter rather than as a note on the ordinary ounce page.

The formula

Multiply troy ounces by exactly 31.1034768. The constant is exact because the troy ounce is defined as 480 grains and the grain is exactly 64.79891 milligrams — both definitions, so the product carries no measurement uncertainty at all. The reverse divides by the same figure, and a round trip through this tool returns your starting value precisely.

Worked examples

One troy ounce is 31.10 g. A ten-ounce silver bar is 311.03 g. A hundred troy ounces is 3,110.35 g, or 3.11 kg. The large gold bars traded in London are nominally 400 troy ounces, which is about 12.44 kg — though the permitted range is wider than the nominal figure, so each bar carries its own assayed weight and 400 describes a convention rather than a guaranteed mass.

Troy against avoirdupois

A troy ounce is 31.1034768 g; an avoirdupois ounce is 28.349523125 g. The troy ounce is about 9.7 percent heavier. That single fact governs a great deal of practical harm: valuing scrap gold with the kitchen ounce, or reading a bullion price against an avoirdupois weight, misprices the metal by that margin in whichever direction disadvantages whoever made the mistake. The units share a name and nothing else, and no amount of care about decimal places compensates for using the wrong one.

Why precious metals kept troy

The troy system was the standard for precious metals and coinage in England from the medieval period, and it survived because the bullion market had no reason to abandon a unit that worked and every reason to avoid re-pricing centuries of contracts and records. When the avoirdupois system displaced troy in general commerce, precious metals simply stayed put. The result is a unit that is universal within its domain and absent everywhere else, which is exactly the sort of arrangement that generates conversion errors at the boundary.

Where the troy ounce still appears

Spot prices for gold, silver, platinum and palladium are quoted per troy ounce on every major market. Bullion coins are minted to round troy weights — one ounce, half an ounce, a tenth. Assay certificates and refinery outputs use it. Futures contracts are denominated in it. Outside precious metals it survives only in historical documents and in a little numismatic usage, which means encountering a troy ounce in any modern context is a reliable indication that the subject is metal.

The troy system in full

A troy ounce is 480 grains. Twenty pennyweights make a troy ounce, so a pennyweight is 24 grains. Twelve troy ounces make a troy pound, which is 373.2417216 g — lighter than the avoirdupois pound despite the troy ounce being heavier, because twelve larger ounces still come to less than sixteen smaller ones. That inversion is the most confusing feature of the two systems coexisting, and it catches people who reason from the ounce relationship to the pound one.

Precision in bullion

Bullion dealers commonly quote three decimal places of a troy ounce, which is about 31 milligrams. At precious-metal prices that is a quantity worth resolving, which is why the scales used are considerably better than the ones behind a shop counter. For a physical bar the assayed weight on the certificate is the operative figure rather than any nominal one, and a converted number should never override an assay.

Common mistakes

Using the avoirdupois ounce for metal, which is the expensive one. Assuming a troy pound is heavier than an ordinary pound because the troy ounce is heavier — it is not. Treating a nominal bar weight as an exact one when the certificate says otherwise. And converting a purity figure as though it were a mass: fineness and karat describe how much of a mass is precious metal, and neither converts on this page.

Benchmarks

0.1 oz t is 3.11 g. 0.5 oz t is 15.55 g. 1 oz t is 31.10 g. 5 oz t is 155.52 g. 10 oz t is 311.03 g. 32.1507 oz t is about 1 kg. 100 oz t is 3.11 kg. 400 oz t is about 12.44 kg. The kilogram at roughly 32.15 troy ounces is the anchor that connects the trade unit to the metric world.

Accuracy and limits

Exact factor, exact decimal arithmetic, display-only rounding, and refusal of ambiguous input with an explanation. The tool converts mass — not value, not fineness, and not the avoirdupois ounce, which has its own pages precisely so the two can never be confused.

Fineness, and why mass alone does not price metal

A troy ounce of 18-karat gold is a troy ounce of mass, of which 18 parts in 24 is fine gold and the rest is alloy. Applying a spot price to the gross mass values the alloy as gold. The sequence that works is: convert the mass, apply the fineness to get the fine metal content, then apply the price. Fineness is expressed as karat for jewellery and as parts per thousand for bullion, where 999.9 is the common refined standard, and neither figure is a mass that any converter can supply.

Silver, and the scale problem

The troy ounce works well for gold, where a few ounces is a meaningful holding, and awkwardly for silver, where holdings run to thousands of ounces. A 1,000 oz silver bar is about 31.1 kg, and industrial quantities are more naturally discussed in kilograms or tonnes. The unit does not change — a troy ounce of silver is the same mass as a troy ounce of gold — but the readable unit for the quantity does, which is why silver figures cross into metric far more often than gold ones.

Reading a bar or a certificate

A physical bar carries an assayed weight and a fineness stamp, and both are needed to know what it contains. The assayed weight is the mass; the fineness says what proportion of that mass is precious metal. A bar stamped 999.9 is refined metal and its mass is effectively its content; a bar of lower fineness is not. Converting the stamped troy weight to grams gives the mass for shipping and customs, and the fine content is a separate multiplication that this page deliberately leaves to you.