Troy Ounce vs. Ounce
$59.76 per troy ounce (31.1035 g)
A food ounce (28.35 g) of pure silver is worth $54.47
Silver spot $59.76/oz · updated
Quick answer: Silver is priced per troy ounce, which weighs 31.1035 grams. The ounce on a kitchen scale weighs 28.3495 grams, so a troy ounce is 9.7 percent heavier. Apply the current silver price per ounce, $59.76, only to troy ounces, or your total will come out too high.
The mistake, with numbers
Picture a small silver bar you have weighed on a kitchen scale. The display reads two ounces. It is tempting to take the live price, $59.76, and multiply by two.
That answer is $119.52. It is wrong, and the reason is the unit. The scale was measuring in food ounces, each of which is 28.3495 grams. Two of them weigh 56.699 grams. Silver is priced by the troy ounce, and 56.699 grams is only 1.8229 troy ounces.
Value that weight correctly and you get $108.94. The sloppy calculation overstated the piece by $10.58.
That gap is not a rounding quirk. It is 8.9 percent, the amount by which a food ounce is lighter than a troy ounce, and it applies to every piece you weigh at home. The error always runs the same direction: if you use the wrong ounce on a scale reading, you always overestimate what the silver is worth.
The simplest defense is to weigh in grams and work from the gram value, which removes the question of which ounce anyone means.
Two ounces, two weights
An ounce is a unit of weight with two common meanings in the United States.
- The avoirdupois ounce is the one used for groceries, postage and body weight. It is 28.3495 grams. Sixteen of them make a pound.
- The troy ounce is used for precious metals. It is 31.1035 grams, or 480 grains, and twelve of them make a troy pound.
The grain is the shared building block. NIST's Handbook 44 lists the troy ounce as 480 grains. An avoirdupois pound is 7,000 grains, so a food ounce is a sixteenth of that, or 437.5 grains. Both systems count in grains; they just group them differently.
| Unit | System | Grains | Grams |
|---|---|---|---|
| Troy ounce | Troy | 480 | 31.1035 |
| Troy pound (12 troy oz) | Troy | 5,760 | about 373.24 |
| Avoirdupois ounce | Avoirdupois | 437.5 | 28.3495 |
| Avoirdupois pound (16 oz) | Avoirdupois | 7,000 | about 453.59 |
The pounds are a trap of their own. A troy pound is lighter than a pound of flour, even though a troy ounce is heavier than an ounce of flour. Twelve ounces to the pound against sixteen is why.
Seeing it on the live price
Here is every unit you are likely to meet, valued at today's silver price. Each row refers to pure silver.
| Unit | Grams | Troy oz | Pure silver |
|---|---|---|---|
| Troy ounce | 31.1035 g | 1.0000 | $59.76 |
| Avoirdupois (food) ounce | 28.3495 g | 0.9115 | $54.47 |
| Gram | 1.0000 g | 0.0322 | $1.92 |
| Kilogram | 1,000.0000 g | 32.1507 | $1,921.33 |
The troy ounce row equals the headline price. The food ounce row is smaller, by 8.9 percent. Gram and kilo rows follow from the conversions; the pages on silver price per gram and silver price per kilo work through each one.
A number worth keeping in mind: a troy ounce is 9.7 percent heavier than a food ounce, but a food ounce is only 8.9 percent lighter than a troy one. The two percentages differ because each is measured against a different starting weight.
Where the name comes from
Nobody can say for certain. The most common account is that "troy" probably comes from Troyes, a French town whose fairs English merchants attended in the Middle Ages. That is likely rather than proven, and the sources we read do not agree on the details, so we leave dates out. What we can say with confidence is that this is a centuries-old English system of weights that was adopted for precious metals and is still how they are priced.
The practical lesson does not depend on the history. The system survived because metal traders needed one fixed weight, and it still serves that purpose.
How to read a label on a coin or bar
Start with the words and numbers stamped on the piece.
- A weight claim. "1 oz" on a bullion coin or bar means one troy ounce of silver. The American Silver Eagle, for instance, is inscribed "1 Oz. Fine Silver", weighs 31.103 grams, and is described in federal law as .999 fine. Details are on the page about the silver Eagle price.
- A purity mark. A number such as .999 or .925 is the share of the weight that is silver. A piece marked .925 is sterling, which is 92.5 percent silver.
- Weight in grams. If the label gives grams, ignore ounces and use the gram price. That avoids the whole question.
If a label says only "ounce" and the piece is jewelry, flatware or a collectible, check whether the seller means troy. Silver pieces weighed in ordinary ounces appear all the time in estate sales and online listings, and an unlabeled "ounce" is a reason to ask.
Weigh the item yourself on a scale that reads in grams. A kitchen scale will do for a rough result, and a result in grams lets you convert with 31.1035 without any doubt about which ounce was meant.
Quick conversion rules
- Troy ounces to grams: multiply by 31.1035.
- Grams to troy ounces: divide by 31.1035.
- Food ounces to grams: multiply by 28.3495.
- Food ounces to troy ounces: multiply by about 0.911, which is the ratio of the two weights.
- Kilograms to troy ounces: multiply by 32.1507.
For a ready-made calculator that takes weight and purity together, use the silver melt value calculator. To see what one troy ounce is worth after the dealer's markup as well, read how much 1 oz of silver is worth.
What this can't tell you
What this can't tell you: whether a given piece is worth owning, what a dealer would offer for it, or what silver will do next. The figures here assume pure silver and the live spot price, and the dealer's buy and sell prices are a separate matter.
Frequently asked questions
Is a troy ounce heavier than a regular ounce?
Yes. A troy ounce is 31.1035 grams and a regular, or avoirdupois, ounce is 28.3495 grams, so the troy ounce is 9.7 percent heavier. Silver and gold are priced in troy ounces; groceries and kitchen scales use the lighter one.
Why is silver priced in troy ounces?
It is a long-standing convention in the metals trade, inherited from an old English weight system for precious metals. Markets still quote spot silver per troy ounce, so every unit conversion on this site starts there, even when the result is shown in grams.
What is a troy ounce in grams?
The rounded figure is 31.1035 grams. The exact definition works out to a little over 31.1034 grams, since the troy ounce is 480 grains. For everyday pricing, 31.1035 is precise enough for any home calculation.
Can I use a kitchen scale to value silver?
You can, but read it in grams, not ounces. A reading in food ounces needs conversion first, because each is 28.3495 grams. Multiply grams by the gram price, $1.92, and then adjust for purity.
Keep going
Once the units are settled, check today's silver spot price and apply it to the right weight. The pages below follow from here.
Sources and further reading
Keep reading
Data sources: Spot price via api.gold-api.com · COMEX futures (SI=F) via Yahoo Finance. Prices are for informational purposes only and may be delayed. Figures on this page were generated . Silver is quoted in US dollars per troy ounce.