GoldInvestingHow Many Grams in a Troy Ounce, and Why Gold Uses It
A troy ounce of gold is exactly 31.1034768 grams, about 9.7% heavier than a kitchen-scale ounce. Troy vs regular ounces, pennyweights, kilos and tolas.
There are 31.1034768 grams in a troy ounce, the ounce gold is weighed in. That's about 9.7% more than the ordinary (avoirdupois) ounce of 28.349523125 grams, and any gold price quoted "per ounce" means the heavier troy ounce.
How many grams are in an ounce of gold?
31.1034768. The figure comes from the U.S. National Institute of Standards and Technology (NIST), whose tables in Handbook 44 and its precious metals conversion sheet give the troy ounce as 31.103 476 8 grams. Nobody rounded it to get there. NIST defines the grain as exactly 64.79891 milligrams, and a troy ounce is 480 grains.
Use the full figure when you price gold. NIST's own worked example gets from a price per troy ounce to a price per gram by dividing by 31.1034768, so with spot at today’s spot price per troy ounce today, a gram of pure gold is that divided by 31.1034768. The gold unit converter handles any weight.
Gold unit converterTroy ounces, grams, kilos, pennyweight and tola. Troy ounce versus the everyday ounce
The ounce in a recipe or on a postal scale is the avoirdupois ounce, which NIST defines as 28.349523125 grams, or 437.5 grains. A troy ounce is 480 grains. Since the grain is the same in both systems, the comparison is neat: a troy ounce has 42.5 more grains.
| Unit | Grains | Grams | Used for |
|---|---|---|---|
| Troy ounce (oz t) | 480 | 31.1034768 | Gold, silver, platinum |
| Avoirdupois ounce (oz) | 437.5 | 28.349523125 | Everyday goods |
| Troy pound (lb t) | 5,760 | 373.2417216 | 12 troy ounces |
| Avoirdupois pound (lb) | 7,000 | 453.59237 | 16 avoirdupois ounces |
| Pennyweight (dwt) | 24 | 1.55517384 | Jewelry and scrap gold |
| Grain (gr) | 1 | 0.06479891 | Same in both systems |
Two things catch people out. A troy ounce is heavier than a regular ounce, at 1.097143 avoirdupois ounces, so a 1 oz gold bar reads about 1.1 ounces on a kitchen scale. Yet a troy pound is lighter than a regular pound, because it has only 12 ounces: 373.24 grams against 453.59. A regular pound of gold holds 14.583 troy ounces.
So if someone weighs gold on an ordinary scale and quotes you ounces, they're the lighter kind. One avoirdupois ounce of gold is only 0.9115 troy ounces.
The pennyweight, a twentieth of a troy ounce
A twentieth of a troy ounce: 24 grains, or 1.55517384 grams. You'll mostly see it on a gold buyer's scale when jewelry gets weighed. NIST's conversion sheet shows how to price it. Divide the price per troy ounce by 20 for the price per pennyweight, then multiply by the item's weight in pennyweights. To turn grams into pennyweights, multiply by 0.6430149.
Jewelry is rarely pure, so karat matters as well. NIST's sheet notes that 24 karat is 99.9% gold, 18 karat is 75% and 12 karat is 50%. The full scale is in gold karats and purity, and selling gold covers how buyers price scrap.
How many troy ounces are in a kilo of gold?
32.15075, by NIST's table. A 1 kilo bar at 999.9 fine holds about 32.15 troy ounces of gold, half a kilo is 16.08, and 100 grams is 3.215.
The big London bars are weighed in troy ounces too. The London Bullion Market Association (LBMA) requires a Good Delivery gold bar to hold between 350 and 430 fine troy ounces, and it records gross weight in troy ounces in steps of 0.025. The gold bars guide lists every common bar size.
The tola, an old unit refiners still use
An old unit that some refiners still use for gold bars. PAMP makes 1, 2, 3 and 5 tola minted bars and a 10 tola cast bar. Valcambi lists its 999.0 fine 10 tola bar at 116.51 grams (3.746 troy ounces) of fine gold, which works out to about 11.66 grams, or 0.375 troy ounces, per tola. That means a 10 tola bar holds a little more gold than a 100 gram bar.
Gold weight conversion table
Every figure uses NIST's factors except the tola row, which is approximate for the reason above.
| Weight | Grams | Troy ounces | Pennyweights | Grains | Avoirdupois ounces |
|---|---|---|---|---|---|
| 1 gram | 1 | 0.0322 | 0.643 | 15.43 | 0.0353 |
| 1 pennyweight | 1.5552 | 0.05 | 1 | 24 | 0.0549 |
| 5 grams | 5 | 0.1608 | 3.215 | 77.16 | 0.1764 |
| 10 grams | 10 | 0.3215 | 6.430 | 154.32 | 0.3527 |
| 1 tola (approx.) | 11.66 | 0.375 | 7.5 | 180 | 0.411 |
| 1 avoirdupois ounce | 28.3495 | 0.9115 | 18.229 | 437.5 | 1 |
| 1 troy ounce | 31.1035 | 1 | 20 | 480 | 1.0971 |
| 50 grams | 50 | 1.6075 | 32.151 | 771.62 | 1.7637 |
| 100 grams | 100 | 3.2151 | 64.301 | 1,543.24 | 3.5274 |
| 10 troy ounces | 311.0348 | 10 | 200 | 4,800 | 10.9714 |
| 1 troy pound | 373.2417 | 12 | 240 | 5,760 | 13.1657 |
| 1 avoirdupois pound | 453.5924 | 14.5833 | 291.667 | 7,000 | 16 |
| 1 kilogram | 1,000 | 32.1507 | 643.015 | 15,432.36 | 35.2740 |
Why gold is weighed in troy ounces
U.S. law requires it, and the big trading markets price in it.
In the U.S. it goes back to the Mint. NIST's history records that on May 19, 1828, Congress adopted the troy pound as the standard for coinage, and a brass troy pound weight brought from London and kept at the Philadelphia Mint became the standard troy pound of the U.S. Mint. NIST notes it became the de facto mass standard for the country.
The current rule sits in NIST Handbook 130. Its Method of Sale of Commodities Regulation, quoted on NIST's precious metals conversion sheet, says that when precious metals are priced in whole or in part by weight, the unit must be troy weight or metric (SI) units. A seller using metric units has to display a conversion chart to troy units so buyers can compare prices, along with a table of troy grains, pennyweights and ounces.
Then there are the trading markets. CME Group's main COMEX gold futures contract is 100 troy ounces, quoted in U.S. dollars and cents per troy ounce, and the LBMA sizes London Good Delivery bars in fine troy ounces. That's why every gold price you see, including the live gold price on this site, is per troy ounce.
Other troy ounce conversions people look up
How many grams are in an ounce of gold?
31.1034768 grams. Gold is weighed in troy ounces, and that's NIST's exact value for one.
Is a troy ounce the same as an ounce?
No. A troy ounce is 31.1034768 grams and a regular (avoirdupois) ounce is 28.349523125 grams, so the troy ounce is about 9.7% heavier.
How many troy ounces are in a pound?
A regular avoirdupois pound holds 14.583 troy ounces. A troy pound holds 12.
How many troy ounces are in a kilo?
32.15075 troy ounces, per NIST.
How many pennyweights are in a troy ounce?
20. One pennyweight is 24 grains, or 1.55517384 grams.
How much is one troy ounce of gold worth?
The spot price, today’s spot price today. The gold price page has the live figure and the gold value calculator handles other weights.
Sources and fact-check9 primary sources, checked October 17, 2026
- NIST: Handbook 44 (2024), Appendix C, General Tables of Units of Measurement
- NIST Office of Weights and Measures: Conversion Factors for Precious Metal Sales (citing Handbook 130, Method of Sale of Commodities Regulation, section 2.17)
- NIST: Special Publication 811, Appendix B.9, Conversion factors for mass
- NIST: 2015 Final Reports, General (history of U.S. measurement standards, May 19, 1828)
- CME Group: Gold Futures Contract Specs
- LBMA: The OTC Guide, London Good Delivery gold and silver
- Valcambi: Cast bars (10 tola bar specification)
- PAMP: Cast bars
- PAMP: Lady Fortuna Gold Minted Bar, 1 tola
We check every figure against the original source: the mint, the regulator, the exchange or the company itself. Spotted something out of date? Tell us.
