Bullion weights explained: grams, troy ounces, and kilos
Why bullion uses the troy ounce, how to convert grams and kilos, and why fractional pieces cost the most per ounce.
Bullion is priced by the troy ounce — 31.1035 grams — not the standard grocery ounce (28.35 g). A troy ounce is about 10% heavier, which trips up a lot of first-time buyers. Products come in grams (1 g to 1 kilo), fractional ounces (1/20 up to 1/2), and full ounces (1 oz to 100 oz). The key rule: premium per ounce generally rises as pieces get smaller. Here are the conversions, and why weight is the biggest lever on what you pay over spot.
The conversions you actually need
| Unit | Equals |
|---|---|
| 1 troy ounce | 31.1035 grams (the bullion standard) |
| 1 standard (avoirdupois) ounce | 28.35 grams — not used for metal pricing |
| 1 gram | 0.0322 troy oz |
| 1 kilogram (1,000 g) | 32.1507 troy oz |
| 1/10 oz · 1/4 oz · 1/2 oz | Common fractional gold sizes — higher premium per ounce |
Why weight drives the premium
Minting, handling, assay, and packaging cost roughly the same per piece no matter the size. On a big bar, that fixed cost is spread over many ounces, so the premium per ounce is small. On a tiny 1/10 oz coin, the same fixed cost lands on a fraction of an ounce, so the premium per ounce is large — often several times a 1 oz coin's. This is why the cheapest-by-weight board shows premiums climbing steadily as you move from kilos down to grams and fractionals.
The practical takeaway: buy the largest weight that fits your budget and divisibility needs. Fractionals are useful for gifting or small, flexible amounts, but you pay a real premium for that convenience.
A quick conversion example
Pricing a 20 gram gold bar, with gold spot at $4,000/oz:
- Weight in troy oz = 20 ÷ 31.1035 = 0.643 oz.
- Metal value = 0.643 × $4,000 = $2,572.
- If the bar is listed at $2,700, the premium is $128 ÷ $2,572 = ~5% over spot.
StackerSpot does this conversion for every product automatically and normalizes each to a per-troy-ounce basis — see the step-by-step in how to calculate premium over spot.
What to verify before you buy
- Troy vs standard — bullion weights are always troy; don't convert with the grocery ounce.
- Gram pricing — convert gram items to per-ounce before comparing to coins.
- Divisibility vs premium — smaller pieces cost more per ounce; buy the largest size that suits you.
See premium by weight, live
Every size normalized per ounce and ranked by premium over spot.
Common questions
Is a troy ounce the same as a regular ounce?
No. Bullion is measured in troy ounces. One troy ounce is 31.1035 grams, while the standard (avoirdupois) ounce used for food and everyday items is 28.35 grams. A troy ounce is about 10% heavier, so never assume a 'gram-to-ounce' conversion using the everyday ounce when pricing metal.
How many grams are in a troy ounce?
31.1035 grams. To convert a gram price to a per-troy-ounce price, divide the total price by the item's weight in grams, then multiply by 31.1035.
How many troy ounces are in a kilo of gold or silver?
A one-kilogram (1,000 g) bar contains 32.1507 troy ounces. Kilo bars — common in silver and in larger gold — usually carry one of the lowest premiums per ounce because their fixed fabrication cost is spread across many ounces.
Why do smaller bullion pieces cost more per ounce?
Minting, handling, and packaging cost roughly the same per piece regardless of size, so those fixed costs are a big share of a small fractional coin and a tiny share of a large bar. That's why a 1/10 oz coin's premium per ounce is far higher than a 1 oz coin's, and why bars get cheaper per ounce as they get bigger.
Methodology & sources
Unit definitions follow standard market conventions (1 troy ounce = 31.1035 g; 1 kg = 32.1507 troy oz). Premiums are computed live from StackerSpot's dealer data on a per-troy-ounce, cash/wire basis against current spot — see the methodology. The conversion example uses round hypothetical numbers. Related: how much over spot you should pay.
Informational purposes only — not investment, financial, or tax advice, and not a licensed dealer or advisor. Prices are each dealer's cash/wire figure, change constantly, and may differ from the dealer's own site; always confirm before buying. See our methodology & disclaimer.