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Troy Ounces to Grams Converter
This troy ounces to grams converter turns troy ounces into grams and back again, and it also handles regular avoirdupois ounces, kilograms, and grains, so you can compare any precious-metal weight in the unit you need. Enter a weight, pick the units, and the answer appears at once. Gold, silver, and platinum are priced by the troy ounce, so getting the troy ounce right matters — a troy ounce is about 10 percent heavier than the everyday ounce, and mixing them up gives a wrong weight and a wrong price.
1 troy ounce = 31.1034768 g = 480 grains. A regular ounce is lighter: 28.3495231 g.
How it works
The troy ounce comes from the troy weight system, which began in the French market town of Troyes in the Middle Ages and became the standard for weighing precious metals and gemstones. One troy ounce is defined as exactly 480 grains, and one grain is 0.06479891 grams, so one troy ounce is 480 × 0.06479891 = 31.1034768 grams. That figure is exact by definition, and this converter uses it in full, rounding only for display.
The key point is that a troy ounce is not the same as the ordinary ounce on a kitchen scale. The ordinary ounce — the avoirdupois ounce — is 28.3495231 grams, which makes the troy ounce about 2.75 grams heavier, or roughly 10 percent. The two systems even count differently: a troy pound has 12 troy ounces, while an avoirdupois pound has 16 ordinary ounces. A troy pound is actually lighter than an ordinary pound, even though a troy ounce is heavier than an ordinary ounce. It is a confusing pair of systems, and the confusion has real consequences when gold is priced by the troy ounce.
Converting is a single multiplication or division. To turn troy ounces into grams, multiply by 31.1034768: 5 troy ounces is 5 × 31.1034768 = 155.52 grams. To turn grams into troy ounces, divide by the same number: 100 grams is 100 ÷ 31.1034768 = 3.215 troy ounces. Kilograms fit in the same way, since one kilogram is 1,000 grams: one kilogram is 32.1507 troy ounces, so a standard one-kilo gold bar is about 32.15 troy ounces. The converter runs every conversion through grams as the common base, which keeps all five units consistent in both directions.
In practice, the troy ounce is the unit of the gold and silver trade. Spot prices are quoted per troy ounce, coins such as the one-ounce gold coin contain exactly one troy ounce of metal, and dealers buy and sell by the troy ounce. If you weigh a gold coin on a kitchen scale and read 31.10 grams, that is one troy ounce — but if the scale shows ounces, it will read about 1.097 ordinary ounces, not 1. Knowing which ounce you are looking at is the whole point of this converter.
Worked example
A jeweller has a small gold bar stamped 5 oz t and wants to know its weight in grams for a customer who thinks in metric. Here is how the converter works it out.
Step 1: Type 5 into the amount box.
Step 2: Leave the From unit on Troy ounces (oz t) and set the To unit to Grams (g).
Step 3: Multiply 5 by 31.1034768, which gives 155.517384 grams.
Step 4: Read the breakdown: 155.52 grams, which is also 0.1555 kg, 5.4857 ordinary ounces, and 2,400 grains.
The tool gives exactly this result: 155.52 grams — 5 oz t = 155.5174 g. Try a second weight: enter 100 in the amount, switch From to Grams (g) and To to Troy ounces (oz t), and the tool gives 3.2151 troy ounces — 100 g = 3.2151 oz t.
FAQ
How many grams are in a troy ounce?
One troy ounce is 31.1034768 grams, usually rounded to 31.10 grams. So 5 troy ounces is 5 × 31.1034768 = 155.52 grams, and 10 troy ounces is 311.03 grams. To go the other way, divide grams by 31.1034768: 100 grams is about 3.215 troy ounces.
Is a troy ounce the same as a regular ounce?
No. A troy ounce is 31.1034768 grams, while a regular avoirdupois ounce — the one used for food and everyday weights — is 28.3495231 grams. The troy ounce is about 10 percent heavier. Using the wrong ounce for gold or silver gives a wrong weight and a wrong price, so always check which ounce a figure uses.
Why is gold weighed in troy ounces?
Gold, silver, platinum and gemstones have been weighed in troy ounces for centuries, since the system began in the French town of Troyes in the Middle Ages. The tradition stuck because the whole precious-metals trade — mines, refineries, dealers and exchanges — quotes prices per troy ounce, so everyone in the trade uses the same unit.
How many troy ounces are in a kilogram?
One kilogram is 32.1507466 troy ounces. A standard one-kilo gold bar is therefore about 32.15 troy ounces. The other way round, one troy ounce is 0.0311034768 kilograms.
How many grains are in a troy ounce?
There are exactly 480 grains in one troy ounce. The grain is the smallest unit in the troy system, and it is also used for gunpowder, arrows and medicine. One grain is 0.06479891 grams, so 480 grains is 480 × 0.06479891 = 31.1034768 grams, which is one troy ounce.