Troy Ounce (oz t)

The troy ounce (symbol oz t) is the mass unit in which gold, silver, platinum and palladium are priced, settled and recorded across the wholesale market. It equals exactly 31.1034768 grams. It sits outside the metric system, and it is not the ounce used for groceries or postage — the avoirdupois ounce of 28.349523125 grams. The two units are close enough that confusing them mis-states the value of a holding by roughly ten percent, which is why every bullion contract, weight list and vault record specifies the troy ounce and nothing else. The distinction that matters most in practice is not troy-versus-avoirdupois but gross-versus-fine: a bar’s troy-ounce figure is reported twice — once for total weight, once for pure-metal content — and only the fine figure is priced and owned.

Exact definition and conversions

The troy ounce is defined through its smallest unit, the grain. Since the international yard and pound agreement of 1 July 1959, the grain is exactly 64.79891 milligrams, so one troy ounce is 480 grains × 0.06479891 = 31.10347680 grams.[1] Above the grain, the system runs: 24 grains to a pennyweight (dwt, 1.55517384 g), 20 pennyweights to a troy ounce, and 12 troy ounces to a troy pound (5,760 grains, 373.2417216 g).

A subtlety that catches non-specialists: the troy pound is lighter than the avoirdupois pound (373.24 g versus 453.59 g) even though the troy ounce is heavier than the avoirdupois ounce — because a troy pound holds twelve ounces, not sixteen. The grain itself is identical in both systems, which is what makes the two ounces (480 grains versus 437.5) exactly comparable.

Working conversions:

• 1 troy ounce = 31.1034768 g = 0.0311034768 kg
• 1 kilogram = 32.1507466 troy ounces
• 1 tonne = 32,150.7466 troy ounces
• 1 troy ounce = 1.09714 avoirdupois ounces

A common and costly error is dividing a per-kilogram price by 31.1034768 to get a per-ounce price. The correct operation is to multiply the per-kilogram price by 0.0311034768; dividing produces a number that looks plausible and is always wrong.

Gross weight versus fine weight

Bullion is recorded in two weights, and the difference governs valuation. Gross troy ounces (GTO) is the total weight of the bar. Fine troy ounces (FTO) is the pure-gold content: GTO multiplied by the assayed fineness. Settlement, invoicing and ownership run on the fine figure.

A London Good Delivery bar makes the point. Its nominal “400 oz” is a gross approximation; the bar’s gross weight is multiplied by its assay — shown to four decimal places — to give the rounded fine weight that is actually traded.[2] A 400-ounce bar assayed at 0.9999 holds 399.96 fine ounces of gold, and 399.96 is the number that is priced and reconciled. The Good Delivery weight band is itself stated in fine metal: minimum 350 fine troy ounces, maximum 430 fine troy ounces,[3] roughly 10.9 to 13.4 kilograms.

For the standard institutional formats and how they are specified, see the 400 oz Good Delivery bar.

How a bar’s weight is fixed

In the London market, a gold bar’s gross weight is expressed in multiples of 0.025 of a troy ounce, rounded down to the nearest 0.025,[3] so only that rounded-down multiple is credited to the holder. The convention comes from the beam balance used to weigh the bars, where one division corresponds to 0.001 of a troy ounce, and a bar must move the needle at least two divisions — weigh at least 0.002 of a troy ounce over the stated 0.025 multiple — to “turn the scale”; if it does not, the recorded weight drops by 0.025.[4] The conversion factor used to move between metric and troy weights is fixed at 1 troy ounce = 0.0311034768 kilograms.[2]

Two consequences follow that an institutional buyer should plan around. First, where a refiner’s stated weight differs from the weight determined by the vault, the vault’s weight is the one recorded,[2] so the vault’s figure supersedes the producer’s stamp. Second, and for the same reason, the LBMA recommends omitting the stamped weight on a Good Delivery bar, because re-weighing in the vault can produce a different figure and create a discrepancy.[5] The current edition of the Good Delivery Rules was published in January 2026.[6]

On the weight list, refinery-origin bars from Heraeus and Argor-Heraeus SA — both accredited refiners whose bars conform to these rules — carry their fine troy ounce weight, and holdings placed into allocated storage coordinated through Brink’s are reconciled against that fine-ounce figure on the Allocation Record. The unit on the certificate, the unit in the vault count, and the unit on the invoice are the same fine troy ounce.

The troy ounce as a settlement and accounting unit

Under ISO 4217, the standard that assigns three-letter codes to the world’s currencies, gold carries its own code — XAU (numeric 959) — with silver XAG, platinum XPT and palladium XPD.[7] The X-prefix denotes a supranational unit, and “AU” is the chemical symbol from the Latin aurum. Each of these codes is defined as one troy ounce of the metal. The practical effect is that bullion sits inside the same systems that track fiat balances, where a treasury or custody ledger holds XAU positions in troy ounces alongside USD or EUR, and spot gold is quoted as XAU/USD — dollars per troy ounce. The troy ounce is the denomination sitting behind the code.

The spot figure that moves continuously in the over-the-counter market is a price per troy ounce; see gold quoted per troy ounce for how that benchmark is formed.

Allocated versus unallocated ounces under Basel III

The same troy ounce can carry a different regulatory weight depending on how it is held. Under the Basel III Net Stable Funding Ratio, physical and unallocated gold on a bank’s balance sheet attracts an 85% Required Stable Funding factor[8] — for every 100 units of unallocated gold a bank holds, it must carry 85 units of stable funding against it. Allocated gold is treated differently: it sits off the custodian’s balance sheet, carries no counterparty credit risk, and is a Tier 1 asset with a zero risk weighting.[9] The rule, phased in across the EU, the UK and Switzerland in 2021–2022, has pushed bank holdings structurally toward allocated metal. The unit of account throughout is the fine troy ounce; what changes is whether those ounces are specific, identified, client-owned bars or an unallocated claim. This is one reason the allocated/unallocated distinction is a substantive matter for institutional holders rather than a formality.

The troy ounce on a futures exchange

On COMEX, the benchmark gold contract (GC) is built on the unit. The contract is one hundred troy ounces, the minimum price fluctuation is ten cents per troy ounce, and delivery is satisfied by one 100-troy-ounce bar or three one-kilogram bars,[10] at a minimum 995 fineness. The Enhanced Delivery contract (4GC) widens the deliverable formats to 100-ounce, 400-ounce and kilo bars,[11] and smaller E-mini (50 oz) and E-micro (10 oz) contracts exist, the latter delivering a certificate representing a ten-percent interest in a 100-ounce bar.

The exchange’s precision is exact and recently tightened: from May 2025 the approved depository weighs each 100-ounce bar to one-thousandth of a troy ounce, and metric weights are converted to troy ounces by dividing grams by 31.1035 and rounding to the nearest thousandth, with all documentation expressed in troy ounces.[12] Among the depositories approved to hold gold deliverable against COMEX contracts is Brink’s, the same custody operator used for allocated coordination.

Not a single global unit

In China, the Shanghai Gold Exchange quotes its Au99.99 benchmark in renminbi per gram,[13] and the People’s Bank of China switched its Gold Panda coins from troy ounces to integer grams in 2016. India trades the tola (11.6638 g, about 0.375 troy ounce). The Hong Kong corridor runs on the tael, where the Hong Kong tael is 37.429 g, or 1.20337 troy ounces, fixed in statute, and the standard 5-tael Good Delivery bar is 6.01685 troy ounces.[14] A further distinction sits inside the Hong Kong market — the Chinese Gold & Silver Exchange Society set its standard traded gold at 99 fine in 1970,[15] so a Hong Kong Good Delivery tael bar is 990 fineness, below the LBMA’s 995 minimum and the 999.9 “four nines” investment standard. The troy ounce holds the Western and OTC settlement markets, while these regional units govern their home jurisdictions — so a single cross-border transaction can carry a bar weighed in grams in Shanghai, quoted in taels in Hong Kong, and settled in troy ounces in London.

Origin

The history is less settled than most accounts suggest. The origin of the troy weight system is unknown; the name probably derives from the medieval Champagne fairs at Troyes in north-eastern France, and “troy” is first attested in 1390 describing the weight of a platter.[1] The lineage runs back further to the Roman uncia — one-twelfth of a bronze bar of currency weight, the root of the word “ounce.” Troy weights were made official for gold and silver in England in 1527, and Britain abolished the twelve-ounce troy pound in the nineteenth century while retaining the troy ounce for precious metals. The confident statement, common on dealer pages, that the unit simply “originated in Troyes” overstates what the record supports.

Where the unit applies at Golden Ark Reserve

Golden Ark Reserve prices, contracts and records refinery-origin bullion in fine troy ounces. Allocated holdings coordinated through Brink’s are reconciled against the fine-ounce figure on the Allocation Record, and the client-facing Evidence Set is denominated in the same unit, so the weight on the bar list, the vault count and the transaction record reconcile to a single number.

To begin a documented purchase of refinery-origin bullion priced in fine troy ounces, see commercial gold purchase.

Sources

1. Troy weight — Wikipedia
2. Good Delivery Rules, Annex C (Weight Lists) — LBMA
3. Good Delivery Rules, Technical Specifications — LBMA
4. Good Delivery Rules, Annex B (Weighing, Packing and Delivery Procedures) — LBMA
5. The OTC Guide — London Good Delivery, Gold and Silver — LBMA
6. Good Delivery — Wikipedia
7. ISO 4217 currency codes — ISO
8. Basel III: The Net Stable Funding Ratio — Basel Committee on Banking Supervision (BIS)
9. Basel III and the gold market — World Gold Council
10. COMEX Rulebook, Chapter 113 (Gold Futures) — CME Group
11. Gold Enhanced Delivery — CME Group
12. COMEX gold rule amendment, self-certification filing (April 2025) — CFTC
13. Benchmark Price — Shanghai Gold Exchange
14. Tael Bars — Gold Bars Worldwide