Weight and purity conversions for selling silver: the complete guide

Spend five minutes in the silver market and you will hear at least three different units of weight thrown around as if everyone already knows what they mean. They do not always mean what you think, and that gap between what you assume and what the buyer is actually calculating is where sellers lose money quietly, without ever realizing it happened.

This guide lays out every conversion you need, explains why the precious-metals trade uses units that the rest of the world abandoned centuries ago, and flags the specific mistakes that come up again and again when people try to work out what their silver is worth. If you are new to all of this, the FAQ page covers the broader basics of selling silver. This post focuses purely on the numbers.

Why the silver trade does not use regular ounces

The first thing that trips people up is that an "ounce" means something different depending on whether you are weighing a letter or a silver bar. The ounce used in everyday life - on food packaging, postal scales, and recipe books - is the avoirdupois ounce, a unit that dates back to medieval English wool trading. It is roughly 28.35 grams.

The ounce used to price silver (and gold, platinum, and palladium) is the troy ounce, which traces its lineage to the market town of Troyes in medieval France. A troy ounce is 31.1035 grams. That difference of about 2.75 grams sounds small until you scale it up: a pound of silver weighed on your kitchen scale is not a pound of silver in the way a bullion dealer understands the word "pound." Troy weight uses 12 ounces to the pound rather than 16.

Spot price - the live market price you see quoted on financial sites - is always denominated in troy ounces. Every time a buyer quotes you a percentage of spot, they are working from that troy-ounce price. If you accidentally use an avoirdupois ounce in your own calculation, you will underestimate your silver's weight by roughly 9 percent. On a meaningful quantity of silver, that is a real and avoidable error.

The four units you will encounter

Troy ounces (ozt)

The master unit for precious metals pricing worldwide. When a buyer says "I pay 90 percent of spot," the spot price they are referencing is per troy ounce.

• 1 troy ounce = 31.1035 grams
• 1 troy ounce = 20 pennyweight (dwt)
• 1 troy ounce = 1.09711 avoirdupois ounces

The abbreviation is sometimes written "ozt" to distinguish it from the avoirdupois ounce (oz). On bullion products you will also see "t oz" or simply "oz troy."

Grams (g)

Grams are the unit you will see on most digital kitchen scales and jewelry scales. They are metric, unambiguous, and the easiest unit to verify independently with a cheap scale.

• 1 gram = 0.03215 troy ounces
• 1 gram = 0.03527 avoirdupois ounces
• 1 gram = 0.6430 pennyweight (dwt)

To convert grams to troy ounces, divide by 31.1035. That number is worth memorising or writing on a sticky note near wherever you do your weighing. Dividing grams by 31.1 (a simplified version) is accurate enough for most purposes.

Avoirdupois ounces (oz) - the postal-scale ounce

If you do not own a jewelry scale and you reach for the kitchen or postal scale, you are measuring in avoirdupois ounces. The conversion is:

• 1 avoirdupois ounce = 0.9115 troy ounces
• 1 avoirdupois ounce = 28.3495 grams
• 1 avoirdupois ounce = 18.229 pennyweight (dwt)

A practical shortcut: if your postal scale reads in avoirdupois ounces and you want grams, multiply the reading by 28.35. Then divide by 31.1 to get troy ounces. It is two steps, but both use numbers that are easy to key into a phone calculator.

The pennyweight comparison is the one worth sitting with for a moment. One avoirdupois ounce equals roughly 18.2 pennyweight - not 20. If a buyer quotes you a price per pennyweight and you assume 20 pennyweight to the ounce, you are working with the troy-ounce relationship. If your scale is reading avoirdupois ounces, you only have 18.2 pennyweight per reading, not 20. The arithmetic matters.

Pennyweight (dwt)

Pennyweight is the unit you will encounter at pawnshops and jewelry counters. It has a long history in the gold and silver trades and survives because many small buyers built their whole pricing system around it decades ago and never updated their signage. The abbreviation "dwt" comes from the Latin "denarius weight."

• 1 pennyweight = 0.05 troy ounces
• 1 pennyweight = 0.05486 avoirdupois ounces
• 1 pennyweight = 1.5552 grams
• 20 pennyweight = 1 troy ounce

If a buyer offers you a price per pennyweight, multiply that price by 20 to get the equivalent price per troy ounce, then compare it against spot. That single step puts all offers on the same footing so you can compare them fairly.

The conversion that causes the most trouble

The confusion between avoirdupois ounces and troy ounces comes up repeatedly among sellers who are new to the market. Here is a concrete illustration of why it matters.

Suppose silver spot is $30 per troy ounce and you have a sterling silver piece (92.5 percent pure) that weighs 10 avoirdupois ounces on your postal scale.

Incorrect calculation (common mistake): 10 oz x $30 = $300 melt value

Correct calculation: 10 avoirdupois oz x 28.3495 = 283.495 grams 283.495 grams / 31.1035 = 9.115 troy ounces 9.115 troy oz x 0.925 (sterling) x $30 = $252.95 melt value

The difference is nearly $47 in this example - and that is before the buyer's margin. Sellers who walk into a negotiation with the wrong melt value in their head start the conversation at a disadvantage. A buyer who sees you have done your homework is also less likely to try to negotiate aggressively.

For a broader look at the terminology buyers use when they are working out their offers, the plain-English glossary of silver and gold trade terms is worth reading alongside this post.

Understanding purity: fineness and percentage

Weight is only half the calculation. The other half is purity. Silver items are rarely pure silver, and the way purity is expressed varies by context.

Fineness

Fineness expresses purity in parts per thousand. Fine silver - the benchmark - is 999 fine, meaning 999 parts silver out of 1000. Britannia silver is 958 fine. Sterling silver is 925 fine.

To convert fineness to a decimal percentage, divide by 1000. So 925 fine = 0.925 = 92.5 percent silver.

Percentage or decimal

Many buyers and online calculators express purity as a decimal: 0.999, 0.925, 0.800, and so on. These are identical to fineness divided by 1000. When you see a price described as "value in troy ounces x purity x spot," the purity figure is this decimal.

Common silver purities you will encounter

| Item type | Fineness | Decimal | |---|---|---| | Fine / investment silver | 999 | 0.999 | | Britannia (UK hallmark) | 958 | 0.958 | | Sterling (most flatware, jewelry) | 925 | 0.925 | | Continental European silver | 800 | 0.800 | | Mexican silver (older pieces) | 900 | 0.900 | | US coin silver (pre-1965 dimes, quarters) | 900 | 0.900 | | US coin silver (half dollars 1965-1970) | 400 | 0.400 |

The 800 mark is worth flagging separately. A lot of older European flatware and holloware carries an 800 stamp, and sellers sometimes assume it is sterling (925) because it looks the same. The melt value of 800 silver is about 86 percent of the equivalent weight in sterling. On a heavy piece, that gap is meaningful.

If you are trying to identify what you have before approaching a buyer, how to sort an inherited box of silver before getting quotes walks through a sensible process for grouping items by purity category.

Building the full melt-value calculation

Once you have the weight in troy ounces and the purity as a decimal, the formula is straightforward:

Melt value = weight (troy oz) x purity (decimal) x spot price (per troy oz)

Example: You have 15 grams of 800 silver.

1. Convert to troy ounces: 15 / 31.1035 = 0.4824 ozt
2. Apply purity: 0.4824 x 0.800 = 0.3859 ozt of fine silver
3. Apply spot (say $30): 0.3859 x $30 = $11.58 melt value

A buyer will typically offer a percentage of that melt value rather than the full amount, because they have overhead and risk to account for. Understanding the melt value lets you assess whether an offer is reasonable.

It is also worth knowing that melt value is not the only thing that matters. Some silver items carry collector or antique premiums that exceed scrap value. A sterling Georgian tablespoon, for example, might be worth more to a specialist dealer than its silver weight suggests. The melt calculation gives you a floor, not always a ceiling.

Scales and tools that make this easier

A digital jewelry scale that reads in grams is inexpensive and eliminates the avoirdupois/troy confusion entirely. If you weigh in grams, you only need one conversion: divide by 31.1 to get troy ounces. That is simpler and less error-prone than working through a postal scale reading.

When shopping for a scale, look for:

• A capacity of at least 500 grams (larger pieces need this)
• Readability of 0.1 grams or better (0.01g for small jewelry)
• A tare function so you can zero out a container

Calibration matters too. A scale that drifts even slightly can make a material difference across a large lot. Most digital scales include a calibration weight; use it.

If you are checking a buyer's stated weight against your own measurement and they do not match, ask them to re-weigh in front of you or to specify which unit they used. Discrepancies are sometimes honest scale differences, but they can also reflect a unit confusion - or, occasionally, something less innocent.

How purity and weight interact with buyer offers

In practice, buyers often pay a lower percentage of spot for lower-purity silver than for fine bullion. Some buyers pay less relative to spot for 800 continental silver than for fine bullion, since refining lower-purity silver can cost more. Understanding this lets you sort your items before approaching a buyer, which often leads to better outcomes.

If you have a mix of purities in one lot, some buyers may average the purity across the whole batch, which could work against you if you have high-purity pieces mixed in. Presenting items sorted by purity, and asking for a breakdown by category, is a reasonable and legitimate request.

The home page, which covers the fundamentals of selling silver, has guidance on how the overall buying process works if you want that broader context.

Conversion cheat sheet (worth saving)

Here is every conversion in one place:

From troy ounces:

• 1 ozt = 31.1035 g
• 1 ozt = 20 dwt
• 1 ozt = 1.0971 avoirdupois oz

From grams:

• 1 g = 0.03215 ozt
• 1 g = 0.6430 dwt
• 1 g = 0.03527 av oz

From avoirdupois ounces (postal/kitchen scale):

• 1 av oz = 0.9115 ozt
• 1 av oz = 28.3495 g
• 1 av oz = 18.229 dwt

From pennyweight (dwt):

• 1 dwt = 0.05 ozt
• 1 dwt = 1.5552 g
• 1 dwt = 0.05486 av oz

Purity conversion:

• Fineness to decimal: divide by 1000 (e.g. 925 / 1000 = 0.925)
• Decimal to percentage: multiply by 100 (e.g. 0.925 x 100 = 92.5%)

Screenshot this, write it on an index card, or bookmark this page. Having the numbers to hand before you walk into a negotiation costs nothing and is worth a surprising amount.

A final note on doing your own maths

There is nothing wrong with asking a buyer to show you their calculation. Reputable buyers should be willing to explain exactly how they arrived at an offer: the weight they measured, the purity they assigned, the spot price they used, and the percentage of melt they are paying. If any of those steps are unclear or the numbers do not reconcile, that is worth questioning.

The sellers who do best are the ones who come prepared. They know their weight in grams, they know the purity stamped on their pieces, and they can convert both into a melt value before the conversation starts. That preparation does not guarantee the highest possible offer, but it does make it much harder for errors - accidental or otherwise - to go unchallenged.

For more background on what happens to your silver after you sell it, what a refiner actually does with your scrap silver is a useful read. And if you are still at the stage of figuring out what you actually have, where scrap gold and silver hides in an ordinary house might surface items you have not thought to include in your total.

The maths here is not complicated. The only requirement is knowing which units you are working in at each step - and never assuming that an "ounce" is an "ounce" until you have confirmed which kind.

Revision history (1)

• Aug 28, 2026 - Pre-publish editorial QA: 1 flagged, 1 softened; claim audit: 3 claims, 3 rewritten

Claim-by-claim audit (3 checked)

• “In practice, buyers often pay a lower percentage of spot for lower-purity silver than for fine bullion.” (rewritten to what the article can stand behind)
• “Some buyers pay less relative to spot for 800 continental silver than for fine bullion, since refining lower-purity silver can cost more.” (rewritten to what the article can stand behind)
• “If you have a mix of purities in one lot, some buyers may average the purity across the whole batch, which could work against you if you have high-purity pieces mixed in.” (rewritten to what the article can stand behind)