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How Many Grams in an Ounce? Troy vs Avoirdupois
Ask how many grams in an ounce and the honest answer is that it depends on which ounce you mean. An ordinary kitchen ounce is 28.3495 grams and a troy ounce of gold or silver is 31.1035 grams, so the two differ by about 9.7 percent. Picking the wrong one on a bullion trade is expensive. On a 100 gram gold bar, the ounce mix-up alone is about $1,330 at the September 25, 2026 quote of $4,255 per troy ounce.
Why two ounces exist, and why neither is going away
The avoirdupois system comes from Old French words for goods of weight, and it helped standardise everyday trade during the later Middle Ages when merchants needed a common measure. This common system uses sixteen ounces to make a pound, which weighs 453.59 grams. You see this weight on kitchen scales and at post offices because it covers the bulk of retail goods. It stays around because it works.
The troy system is much older and named after the Champagne fair town of Troyes, where medieval merchants set strict standards for precious metals, coins, gems, and medicine. Since a troy pound only has twelve ounces, it weighs less at 373.24 grams than the standard pound. The apothecary ounce once matched this troy weight, but that system is rare now. Bullion never switched to the common scale, so the world still prices metal per troy ounce.
Where each ounce shows up
The avoirdupois system is the standard for almost every common weight you will encounter in the United States or the UK, covering everything from groceries and postage to cosmetics and your own body weight. You'll use this system when you buy food at the store or weigh a package for the post office because it was built for general trade. It's the practical choice for daily life, though it doesn't apply to high-value metals.
Precious metals like gold, silver, platinum, and palladium use the troy ounce for all spot quotes, investment bars, and the LBMA benchmark. You will see these units on bullion coins like the American Gold Eagle, the Canadian Maple Leaf, and the Krugerrand. The same is true when you read the silver price or any other metal quoted per ounce. This system stays relevant in exchange reporting because it provides a consistent standard for high-value assets, which is why the World Gold Council describes troy as the global bullion standard.
If you place a one-troy-ounce coin on a standard kitchen scale, it will read as about 1.097 avoirdupois ounces, which is correct and not a scale fault. This happens because the troy ounce is about 9.7 percent heavier than the common ounce you use for groceries. Mistaking one for the other creates big errors when you try to calculate the value of your metal.
What picking the wrong ounce costs
If you use the standard kitchen ounce to convert the gold price into a per-gram figure, your math lands about 9.7 percent off before you start. At a spot price of around $4,255 per troy ounce, the real cost per gram is $136.81 when you divide by 31.1035 grams. If you mistakenly divide by 28.3495 instead, you get a figure of $150.10 per gram, which is an error of about 9.7 percent.
This small math slip costs you about $1,330 on a simple 100 gram bar, and the loss scales linearly as you buy larger pieces, so the same mistake on a kilogram bar is roughly $13,300. It's common to see a buyer who does the wrong math accuse an honest seller of overcharging them, even though the seller is just using the correct standard. Check the Kitco live quote page to confirm the current numbers before you start your own calculations, and check your divisor before you check the price.
Conversions worth knowing
If you want to buy gold or weigh out flour, you need to know that a troy ounce is 31.10 grams while a standard ounce is only 28.35 grams. The most common conversion questions, carried to two decimal places:
| Quantity | Avoirdupois (everyday) | Troy (precious metals) |
|---|---|---|
| 1/4 ounce | 7.0874 g | 7.7759 g |
| 1/2 ounce | 14.175 g | 15.552 g |
| 3/4 ounce | 21.262 g | 23.328 g |
| 1 ounce | 28.3495 g | 31.1035 g |
| 2 ounces | 56.699 g | 62.207 g |
| 5 ounces | 141.748 g | 155.518 g |
| 10 ounces | 283.495 g | 311.035 g |
| 1 pound (16 avdp oz / 12 troy oz) | 453.59 g | 373.24 g |
| 1 kilogram | 35.274 oz | 32.1507 oz |
You can find the price per gram by dividing the troy price by 31.1035, or you can multiply the troy price by 32.1507 to find the cost of a kilo. A tola is 11.6638 grams and is common in India, Pakistan and the Gulf, where gold rates are quoted per 10 grams, while a baht is 15.244 grams for Thai jewellery. At the $4,255 quote, one tola of gold works out to about $1,596 and one baht to about $2,085. These specific units help when you shop across borders where local standards still rule the market.
Mental shortcuts make the math easier, since a troy ounce is about 31 grams and a kilo is about 32 troy ounces. A tola is about three-eighths of a troy ounce, while an avoirdupois ounce is about 28 grams. These shortcuts err in the safe direction for a buyer because they keep you from overpaying for weight. When the metal is karat-grade jewellery rather than bullion, the purity fraction comes out of the same per-gram figure before you multiply by weight.
Frequently Asked Questions
Is a troy ounce heavier than a regular ounce?
A troy ounce is about 9.7 percent heavier than the standard avoirdupois ounce that people use for measuring groceries and kitchen items. This specific weight system is used for precious metals like gold, silver, and platinum. A troy ounce measures 31.1035 grams while a regular ounce is only 28.3495 grams.
Is 28 grams an ounce?
Twenty-eight grams is close to a regular ounce, but the standard avoirdupois ounce actually measures 28.3495 grams for most retail purposes. If you use 28 grams for a quick calculation, you will miss a small amount of weight. This tiny error becomes a major issue when you buy high-value gold bullion.
How many grams in a half and quarter ounce of gold?
A half troy ounce coin weighs about 15.55 grams, while a quarter troy ounce coin weighs roughly 7.78 grams in total. These fractional units are common for major mints like the American Gold Eagle or Canadian Maple Leaf. You should check these weights if you are buying small gold pieces.
How many grams in a pound?
An avoirdupois pound weighs 453.59 grams, whereas a troy pound is much lighter because it only weighs 373.24 grams. The troy pound contains only twelve ounces instead of the sixteen ounces found in a standard pound. This difference often confuses buyers who are comparing different weight charts.
Why does my kitchen scale show different ounces than the coin label?
Your kitchen scale measures weight in avoirdupois ounces, but gold coins are labeled using troy ounces according to industry standards. A one-troy-ounce coin will register as about 1.097 avoirdupois ounces on a standard digital scale. The gram value is the true mass, and the ounce reading is just the same weight expressed in the other system, so both numbers are correct.
If you find yourself converting between ounces, grams, tolas, and kilos more than once a week, an app that does live conversions in your menu bar takes the math out of the equation. SpotBar shows live spot prices with per-troy-ounce, per-gram, per-tola, and per-kilo display on Pro. The free version is gold-only in US dollars, and Pro is a one-time purchase, no subscription and no account.