Troy Ounce (oz t) - Unit Information & Conversion

Quick Answer

1 troy ounce = 31.1034768 grams (EXACT)

The troy ounce is the global standard for weighing and pricing precious metals—gold, silver, platinum, palladium, and rhodium. It's about 9.7% heavier than the regular (avoirdupois) ounce you use in cooking. When you see "gold price $2,000 per ounce," that's always per troy ounce. Investment coins (American Gold Eagle, Canadian Maple Leaf), bullion bars, and jewelry-grade metals are measured in troy ounces.

Why it matters: If you're buying gold, understanding troy ounces prevents costly mistakes. A 1 oz gold coin contains 1 troy ounce (31.1 g), not 1 avoirdupois ounce (28.35 g)—that's 2.75 grams more gold than a "regular" ounce!

Quick Comparison Table

Measurement	Troy Ounces	Context
Standard gold bar (London Good Delivery)	400 oz t	Central bank reserve standard
American Gold Eagle coin (1 oz)	1 oz t	31.1035 g of 22K gold
Silver Morgan Dollar (historic)	0.77344 oz t	26.73 g pure silver content
Platinum catalytic converter	3-7 oz t	Automotive emission control
Olympic gold medal (minimum)	0.2143 oz t	6+ g gold plating over silver
Wedding ring (14K gold, typical)	0.1-0.2 oz t	3-6 grams
Fort Knox gold reserves	147.3M oz t	U.S. Treasury holdings (~$350B)

Definition

1 troy ounce = 31.1034768 grams (g) = 480 grains

The troy ounce (abbreviated "oz t", "ozt", or "t oz") is a unit of mass in the troy weight system, used exclusively for precious metals and gemstones. It differs significantly from the avoirdupois ounce used in everyday measurements.

Troy vs. Avoirdupois: Critical Distinction

Unit	Grams	Use Cases
Troy ounce	31.1034768 g	Precious metals (gold, silver, platinum), gemstones, pharmaceuticals (historic)
Avoirdupois ounce	28.349523125 g	Food, body weight, general commerce
Difference	+2.754 g (9.7% heavier)	Troy ounce is HEAVIER

Critical for buyers: If someone sells you "1 ounce of gold" using avoirdupois ounces instead of troy ounces, you're getting 9.7% less metal than you paid for!

The Troy Weight System

Unlike the avoirdupois system (16 ounces = 1 pound), the troy system uses different ratios:

• 24 grains = 1 pennyweight (dwt)
• 20 pennyweights = 1 troy ounce (oz t)
• 12 troy ounces = 1 troy pound (lb t)

Paradox: The troy ounce is heavier than the avoirdupois ounce, BUT the troy pound (373.24 g) is lighter than the avoirdupois pound (453.59 g) because it contains only 12 ounces instead of 16!

Why Troy Ounces Persist

Despite global metrication, troy ounces remain dominant in precious metals for these reasons:

1. Market convention: Centuries of gold/silver trading established price benchmarks in troy ounces
2. Legal tender: U.S. Mint, Royal Canadian Mint, and others mint official coins in troy ounce denominations
3. Futures contracts: COMEX gold contracts specify 100 troy ounces per contract
4. LBMA standards: London Bullion Market Association requires troy ounce quotations
5. Central banks: Gold reserves reported in troy ounces (e.g., Fort Knox holds 147.3 million oz t)

History

Ancient and Medieval Origins (Pre-1500)

The word "ounce" derives from the Latin "uncia" (one-twelfth), reflecting the Roman system where 1 uncia = 1/12 of a libra (pound). The troy system's specific origins trace to Troyes, France, a major European trade city.

12th-15th centuries - Champagne Fairs: Troyes hosted international trade fairs where merchants from Italy, Flanders, England, and German states exchanged goods. Precious metals, spices, and textiles required standardized weights. The "Troyes weight" system emerged as a trusted standard for valuable commodities, particularly gold, silver, and gemstones.

Why "troy" not "avoirdupois"? Two parallel weight systems developed:

• Troy weights: For precious metals, spices, medicines (high-value, small quantities)
• Avoirdupois weights: For bulk goods like wool, grain, iron (from French "avoir de pois" = goods of weight)

English Standardization (1500-1800)

1527 - King Henry VIII standardization: Henry VIII officially defined troy weights for the English realm, establishing:

• 1 troy pound = 5,760 grains
• 1 troy ounce = 480 grains
• 1 grain = 64.79891 milligrams (based on barley grain weight)

1758 - British assay offices: The Goldsmiths' Company and assay offices in London, Birmingham, Sheffield, and Edinburgh used troy ounces exclusively for hallmarking gold and silver items. This reinforced troy ounces as the legal standard for precious metals in British commerce.

The Tower Pound obsolescence: England previously used the "Tower pound" for minting coins (5,400 grains), but troy weights (5,760 grains per pound) eventually replaced it in 1527, creating unified standards for bullion and coinage.

American Adoption (1776-1900)

1776-1792 - Early United States: American colonies inherited British troy standards. The early U.S. used Spanish silver dollars and British gold sovereigns, all measured in troy ounces.

1828 - U.S. Coinage Act: Congress officially adopted troy weights for all U.S. coinage. The Act specified:

• Gold dollar = 25.8 grains (1.672 g) of 90% gold
• Silver dollar = 412.5 grains (26.73 g) of 90% silver
• All coins measured in troy grains

1849-1855 - California Gold Rush: The discovery of gold at Sutter's Mill created massive demand for standardized weights. Assay offices in San Francisco weighed gold dust and nuggets in troy ounces, establishing the unit in the American West.

1873 - Coinage Act ("Crime of 1873"): This act demonetized silver, ending bimetallism. However, troy ounces remained the standard for measuring both gold and silver bullion.

Global Standardization (1900-Present)

1900-1971 - The Gold Standard era: Most nations tied currencies to gold reserves, measured in troy ounces:

• 1900: Gold Standard Act (U.S. fixed $20.67 per troy ounce)
• 1933: FDR revalued gold to $35 per troy ounce
• 1944: Bretton Woods Agreement ($35/oz t peg)
• 1971: Nixon ended gold convertibility, but troy ounce pricing persisted

1919 - London Bullion Market Association (LBMA): Founded to standardize London gold market practices. LBMA established:

• Good Delivery bars: 350-430 troy ounces (typically 400 oz t)
• Minimum purity: 995 parts per 1,000 (99.5% pure gold)
• Troy ounce quotations for spot prices

1974 - COMEX gold futures: The Commodity Exchange (COMEX) in New York launched gold futures contracts:

• Contract size: 100 troy ounces
• Delivery specifications: 1 kg bars (32.1507 oz t) or 100 oz bars
• Global price discovery mechanism

1975 - Gold ownership legalization: U.S. citizens regained the right to own gold bullion (banned since 1933). Investment coins like the Krugerrand (1 oz t), Canadian Maple Leaf (1 oz t), and American Gold Eagle (1 oz t) popularized troy ounce denominations for retail investors.

2000s-Present - Digital age: Despite metrication, troy ounces dominate:

• ETFs: SPDR Gold Shares (GLD) holds 900+ tons (28.9M oz t)
• Central banks: Reserve holdings reported in troy ounces (U.S. 261.5M oz t, Germany 108.9M oz t)
• Spot prices: Bloomberg, Reuters, Kitco quote gold/silver per troy ounce
• Refineries: Swiss refiners (PAMP, Valcambi) produce bars in troy ounce sizes

Cultural Significance

The troy ounce represents continuity in global finance—a medieval trade standard that survived the industrial revolution, world wars, and digital transformation. While most historical units vanished with metrication, the troy ounce persists because precious metals markets value tradition, legal precedent, and universal standardization over decimal convenience.

Real-World Examples

1. Investment & Bullion

American Gold Eagle (1 oz):

• Total weight: 1.0909 troy ounces (33.931 g)
• Pure gold content: 1.0000 troy ounces (31.1035 g)
• Alloy: 22 karat (91.67% gold, 3% silver, 5.33% copper)
• Diameter: 32.7 mm
• Face value: $50 USD (legal tender, but worth ~$2,000+ in gold)

London Good Delivery Gold Bar:

• Weight: 400 troy ounces (12.4 kg)
• Purity: Minimum 995/1000 (99.5% gold)
• Dimensions: ~250mm × 70mm × 35mm
• Value: ~$800,000 (at $2,000/oz)
• Used by: Central banks, LBMA vaults, international settlements

Silver Bullion (1 oz rounds):

• Weight: 1 troy ounce (31.1035 g)
• Purity: .999 fine silver (99.9%)
• Common types: Generic rounds, government coins (Silver Eagle, Maple Leaf)
• Typical price: Spot silver + $2-5 premium per ounce

2. Jewelry & Manufacturing

14K Gold Wedding Ring:

• Total weight: 0.15 troy ounces (4.66 g)
• Pure gold content: 0.0875 oz t (2.72 g)—14/24 = 58.3% pure
• Alloy metals: Copper, silver, zinc for durability
• Gold value: ~$175 (at $2,000/oz)
• Retail price: $500-1,500 (labor, design, markup)

18K Gold Rolex Watch (Day-Date):

• Case weight: ~3.5 troy ounces (109 g total)
• Pure gold content: ~2.6 oz t (81 g)—18/24 = 75% pure
• Gold value: ~$5,200 (at $2,000/oz)
• Retail price: $35,000+ (brand, craftsmanship, movement)

Dental Gold Crowns:

• Typical crown: 0.1 troy ounces (3.1 g)
• Alloy composition: 40-70% gold (varies by type)
• Pure gold content: 0.04-0.07 oz t
• Scrap value: $80-140 per crown

3. Coinage & Legal Tender

Canadian Gold Maple Leaf:

• Weight: Exactly 1 troy ounce (31.1035 g)
• Purity: .9999 fine gold (99.99%, "four nines")
• Face value: $50 CAD
• Market value: Spot price + 3-5% premium
• Security features: Radial lines, micro-engraved leaf

Pre-1965 U.S. Silver Coins ("junk silver"):

• Silver quarters (1964 and earlier):
  • Total weight: 0.2 oz t (6.25 g)
  • Pure silver: 0.18084 oz t (90% silver)
  • "Junk silver" value: ~$4.50 per quarter (at $25/oz silver)

Krugerrand (South African 1 oz):

• First modern bullion coin (1967)
• Weight: 1.0909 troy ounces total
• Pure gold: 1.0000 oz t (22 karat, 91.67%)
• Over 60 million sold (most widely held gold coin)

4. Mining & Refining

Gold ore extraction:

• High-grade ore: 10-20 grams per ton (0.32-0.64 oz t per metric ton)
• Low-grade ore: 1-5 g/t (0.032-0.16 oz t/t)
• To produce 1 oz t gold: Process 50-1,000 tons of ore (depending on grade)

Refining output (major refineries):

• Rand Refinery (South Africa): Processes ~30 million oz t gold annually
• PAMP Suisse: Produces gold bars in 1 oz, 10 oz, 100 oz, 1 kg (32.15 oz t) sizes
• Johnson Matthey: Refines platinum group metals, 1 oz t platinum = $1,000+

5. Central Bank Reserves

Top gold holders (2024):

1. United States: 261.5 million oz t (8,133 metric tons)—Fort Knox, West Point, Denver
2. Germany: 108.9 million oz t (3,387 tons)—Bundesbank vaults
3. IMF: 90.5 million oz t (2,814 tons)—International Monetary Fund
4. Italy: 79.0 million oz t (2,452 tons)
5. France: 78.3 million oz t (2,436 tons)

Fort Knox Depository:

• Holdings: 147.3 million troy ounces
• Value: ~$295 billion (at $2,000/oz)
• Storage: 368,000 Good Delivery bars (~400 oz t each)
• Last audit: 1953 (limited inspections since)

6. Industrial Applications

Catalytic converters (automotive):

• Platinum content: 3-7 troy ounces per converter
• Palladium content: 2-7 oz t
• Rhodium content: 1-2 oz t
• Scrap value: $200-1,000+ (recycling industry)

Electronics (gold bonding wires):

• Smartphones: 0.001 troy ounces gold (0.034 g)
• Laptops: 0.003 oz t (0.1 g)
• 1 metric ton e-waste: 10-15 oz t gold (higher grade than ore!)

Silver photography (historic):

• Film processing: 0.05 oz t silver per roll
• X-ray film: 5-10 oz t per 100 sheets
• Kodak reserves: Once held 40+ million oz t silver (1970s)

7. Commodity Trading

COMEX gold futures contract:

• Size: 100 troy ounces
• Tick size: $0.10 per oz = $10 per contract
• Daily volume: 200,000+ contracts (20 million oz t)
• Margin requirement: ~$6,000 per contract (controls $200,000 gold)

Silver futures (COMEX):

• Contract size: 5,000 troy ounces
• Typical price: $25/oz × 5,000 = $125,000 per contract
• Industrial demand: Solar panels (0.67 oz t per panel), EVs, electronics

Common Uses

1. Precious Metals Trading

The troy ounce is the universal standard for global bullion markets:

Spot price quotations:

• Gold: $1,800-2,100 per troy ounce (fluctuates with markets)
• Silver: $20-30 per oz t
• Platinum: $900-1,200 per oz t
• Palladium: $1,000-1,600 per oz t
• Rhodium: $3,000-15,000 per oz t (highest volatility)

Major markets:

• London Bullion Market (LBMA): Sets gold/silver fix twice daily in troy ounces
• COMEX (New York): Futures contracts (100 oz t gold, 5,000 oz t silver)
• Shanghai Gold Exchange: Trades gold in grams but converts to oz t for international quotes
• Dubai Gold Souk: Retail sales in grams, wholesale in troy ounces

Why troy ounces persist: Centuries of price history, legal contracts, and central bank reserves create network effects—changing to grams would require recalibrating trillions in financial instruments.

2. Investment Coins & Bars

Government minted coins (1 oz troy):

• American Gold Eagle: Most popular U.S. bullion coin, 22K gold
• Canadian Maple Leaf: 24K gold (.9999 fine), iconic design
• South African Krugerrand: First modern bullion coin (1967)
• Austrian Philharmonic: European alternative, euro-denominated
• Chinese Gold Panda: Annual design changes, collector value

Fractional coins:

• 1/2 oz, 1/4 oz, 1/10 oz troy ounce denominations
• Higher premiums per ounce (manufacturing costs)
• Easier to liquidate small amounts

Private mint bars:

• 1 oz, 10 oz, 100 oz troy ounce sizes (silver)
• 1 oz, 10 oz, 1 kg gold bars
• Lower premiums than coins (no numismatic value)
• Stackability for storage

3. Jewelry Manufacturing

Jewelers purchase gold in troy ounces but often work in grams or pennyweights (dwt):

Pricing structure:

1. Spot price: Current troy ounce price (e.g., $2,000/oz)
2. Karat adjustment: 14K = 58.3%, 18K = 75%, 22K = 91.67%
3. Fabrication cost: Labor, design, gemstones
4. Retail markup: 2-3× material cost

Example calculation (14K ring):

• Weight: 5 grams = 0.16075 oz t
• Pure gold: 0.16075 × 0.583 = 0.0938 oz t
• Gold value: 0.0938 × $2,000 = $187.60
• Retail price: $500-800 (includes labor, overhead, profit)

Scrap gold recycling: Jewelers sell scrap in troy ounces to refineries, receiving 90-95% of spot price (refining losses, processing fees).

4. Pharmaceutical & Apothecary (Historic)

Before metrication, pharmacists used troy weights for compounding:

Apothecaries' system:

• 20 grains = 1 scruple
• 3 scruples = 1 dram
• 8 drams = 1 troy ounce

Modern legacy:

• Grain measurements persist (aspirin: 5 grains = 325 mg)
• Troy ounces phased out in medicine by 1970s
• Replaced by milligrams and grams for precision

5. Mining & Geology

Gold production and ore grades measured in troy ounces:

Reserve reporting:

• Gold deposits: "10 million oz t at 2 g/t grade" (metric tons ore, troy ounces gold)
• Production rates: "500,000 oz t per year" (annual mine output)

Ore grades:

• High-grade: 10-20 g/t (0.32-0.64 oz t per metric ton ore)
• Low-grade: 1-5 g/t (0.032-0.16 oz t/t)
• Ultra-low-grade: 0.5 g/t (economical with modern extraction)

Example (Nevada Gold Mine):

• Reserves: 50 million metric tons
• Grade: 2 g/t (0.064 oz t/t)
• Contained gold: 3.2 million troy ounces
• Mine life: 15 years (213,000 oz t/year production)

6. Central Banking & Reserves

Countries hold gold reserves measured in troy ounces:

Reserve valuation: Most central banks value gold at historic cost ($42.22/oz t, a 1973 price), not market rates. However, market value uses current spot prices:

• U.S. reserves: 261.5M oz t × $2,000 = $523 billion market value
• Official books: 261.5M oz t × $42.22 = $11 billion (!)

Reserve diversification:

• Gold as % of reserves: U.S. (70%), Germany (67%), Italy (64%)
• Rationale: Inflation hedge, currency crisis protection, geopolitical insurance

7. Collectibles & Numismatics

Coin collectors distinguish between bullion value (troy ounces) and numismatic value (rarity, condition):

Example: 1933 Double Eagle

• Gold content: 0.9675 oz t (~$1,935 melt value)
• Auction price: $18.9 million (2021 Sotheby's)
• Numismatic premium: 9,700× bullion value!

Modern bullion vs. collectible:

• Bullion: Trades at spot + 3-10% premium (1 oz Gold Eagle)
• Collectible: Rare dates, low mintages command 2-100× premiums

Conversion Guide

Basic Conversions

Troy Ounce to Metric:

1 troy ounce = 31.1034768 grams (EXACT)
1 troy ounce = 0.0311034768 kilograms

Troy Ounce to Avoirdupois:

1 troy ounce = 1.09714 avoirdupois ounces
1 avoirdupois ounce = 0.91146 troy ounces

Troy Ounce to Troy Pound:

1 troy pound = 12 troy ounces
1 troy ounce = 0.08333... troy pounds

Troy Ounce to Grains:

1 troy ounce = 480 grains (EXACT)
1 grain = 64.79891 milligrams

Troy Ounce to Pennyweights (dwt):

1 troy ounce = 20 pennyweights (EXACT)
1 pennyweight = 1.55517 grams

Conversion Tables

Troy Ounces → Grams

Troy Ounces	Grams
0.1 oz t	3.11 g
0.25 oz t	7.78 g
0.5 oz t	15.55 g
1 oz t	31.10 g
2 oz t	62.21 g
5 oz t	155.52 g
10 oz t	311.03 g
100 oz t	3,110.35 g (3.11 kg)
400 oz t	12,441.39 g (12.44 kg)

Grams → Troy Ounces

Grams	Troy Ounces
1 g	0.0322 oz t
5 g	0.1608 oz t
10 g	0.3215 oz t
31.1 g	1.00 oz t
50 g	1.607 oz t
100 g	3.215 oz t
500 g	16.075 oz t
1,000 g (1 kg)	32.151 oz t

Troy vs. Avoirdupois Ounces

Troy Ounces	Avoirdupois Oz	Difference
1 oz t	1.097 oz	+2.75 g heavier
5 oz t	5.486 oz	+13.77 g
10 oz t	10.971 oz	+27.54 g
100 oz t	109.714 oz (6.86 lb)	+275.4 g

Practical Conversion Examples

Example 1: Gold bar weight A gold bar weighs 1 kilogram. How many troy ounces?

1 kg = 1,000 g
1,000 g ÷ 31.1034768 g/oz t = 32.1507 troy ounces

Example 2: Silver coin melt value A pre-1965 U.S. quarter contains 0.18084 oz t silver. At $25/oz, what's the melt value?

0.18084 oz t × $25/oz t = $4.52 melt value

Example 3: Jewelry scrap You have 25 grams of 14K gold scrap. Gold spot is $2,000/oz. What's it worth?

Step 1: Convert grams to troy ounces
25 g ÷ 31.1034768 g/oz t = 0.8038 oz t

Step 2: Calculate pure gold content (14K = 58.3%)
0.8038 oz t × 0.583 = 0.4686 oz t pure gold

Step 3: Calculate value
0.4686 oz t × $2,000/oz t = $937.20 value

Example 4: Mining production A mine produces 500,000 troy ounces gold annually. How many kilograms?

500,000 oz t × 31.1034768 g/oz t = 15,551,738.4 g
15,551,738.4 g ÷ 1,000 = 15,551.74 kg (15.55 metric tons)

Common Conversion Mistakes

1. Confusing Troy and Avoirdupois Ounces

The mistake: Treating all "ounces" as equal.

Reality:

• Troy ounce (precious metals) = 31.10 g
• Avoirdupois ounce (food/general) = 28.35 g
• Difference: 9.7% heavier

Costly example: You buy a "16-ounce gold bar" advertised online, assuming 16 troy ounces (497.66 g). If it's actually 16 avoirdupois ounces (453.59 g), you're missing 44 grams of gold—worth ~$2,800 at $2,000/oz!

How to avoid: Always confirm "troy ounces" explicitly. Reputable dealers never use avoirdupois for precious metals.

2. Forgetting Karat Purity in Jewelry

The mistake: Calculating 14K gold jewelry value as if it's 24K pure gold.

Reality:

• 24K = 100% pure gold
• 18K = 75% pure (18/24)
• 14K = 58.3% pure (14/24)
• 10K = 41.7% pure (10/24)

Example error: A 10-gram 14K ring does NOT contain 10 g pure gold.

10 g × 0.583 = 5.83 g pure gold
10 g × (31.1/31.1) ÷ 31.1 = 0.3215 oz t total weight
0.3215 oz t × 0.583 = 0.1874 oz t pure gold
Value: 0.1874 × $2,000 = $374.80 (NOT $643 if you ignore karat)

3. Troy Pound vs. Avoirdupois Pound Confusion

The mistake: Assuming 16 troy ounces = 1 troy pound (wrong!).

Reality:

• Troy pound = 12 troy ounces (373.24 g)
• Avoirdupois pound = 16 avoirdupois ounces (453.59 g)

Paradox: The troy ounce is heavier than the avoirdupois ounce, but the troy pound is LIGHTER than the avoirdupois pound!

Why this confuses people:

1 troy oz (31.10 g) > 1 avoir oz (28.35 g) ✓
BUT
1 troy lb (373.24 g) < 1 avoir lb (453.59 g) ✓

4. Incorrectly Converting Metric Tons to Troy Ounces

The mistake: Using 1 metric ton = 1,000 kg = 32,000 oz t (rounded).

Reality:

1 metric ton = 1,000 kg = 1,000,000 g
1,000,000 g ÷ 31.1034768 g/oz t = 32,150.7466 troy ounces (EXACT)

Why it matters: For large gold reserves, rounding errors compound:

• Fort Knox: 147.3M oz t
• If you used 32,000 oz/t conversion: 4,603 metric tons
• Correct value: 4,582.7 metric tons
• Error: 20.3 tons ($1.3 billion gold!)

5. Mixing Up Spot Price and Premium

The mistake: Thinking a 1 oz Gold Eagle costs exactly the spot price.

Reality:

Spot price: $2,000/oz (what dealers pay for raw gold)
+ Premium: $60-120 (minting, distribution, dealer margin)
= Retail price: $2,060-2,120 per coin

When selling:

Buyback price: Spot price - $20-40 (dealer needs profit margin)
You sell 1 oz Eagle: $1,960-1,980 (even if you paid $2,100)

Avoid: Don't expect to immediately resell coins at purchase price. Buy-sell spreads are ~3-8%.

6. Assuming "1 oz Gold Coin" is 1 oz Total Weight

The mistake: Thinking a 1 oz Gold Eagle weighs exactly 1 troy ounce total.

Reality: Most gold coins are alloyed for durability:

American Gold Eagle (1 oz):

• Pure gold content: 1.0000 oz t (31.1035 g)
• Total weight: 1.0909 oz t (33.931 g)
• Alloy: 22K (91.67% gold + 3% silver + 5.33% copper)

Canadian Gold Maple Leaf (1 oz):

• Pure gold: 1.0000 oz t
• Total weight: 1.0000 oz t (same—24K, .9999 pure)

Why it matters: Eagles weigh more than Maple Leafs despite identical gold content. If you're calculating scrap value for melting, use pure gold content, not total weight!