When you buy a gold coin, bar, or piece of jewelry, it’s marked with a purity indicator that tells you how much actual gold the item contains. Understanding these markings — the karat system and the fineness system — is fundamental to knowing what you’re buying and what it’s worth.
The Two Systems: Karats and Fineness
The Karat System
The karat system (abbreviated “K” or “kt” in American usage, “ct” in British usage) measures gold purity in 24ths — representing the number of parts out of 24 that are pure gold.
| Karat | Gold Content | Percentage | Common Use |
|---|---|---|---|
| 24K | 24/24 | 99.9%+ | Investment bars, some bullion coins |
| 22K | 22/24 | 91.67% | American Gold Eagle coins, Krugerrands |
| 18K | 18/24 | 75.0% | High-end jewelry |
| 14K | 14/24 | 58.33% | Standard jewelry (US) |
| 10K | 10/24 | 41.67% | Economy jewelry (US minimum legal standard) |
| 9K | 9/24 | 37.5% | Common in UK, Ireland, some European countries |
Why jewelry uses lower karats: Pure 24K gold is too soft for most jewelry applications — it scratches easily, bends, and loses its shape. Alloying with copper, silver, palladium, or nickel increases hardness and durability while maintaining gold’s appearance. The tradeoff is reduced gold content.
Why investment products aim for 24K: For investment purposes, maximum gold content means maximum value per ounce purchased. The premium for refining to 24K is minimal compared to the value advantage.
Note on 22K: The American Gold Eagle and South African Krugerrand contain exactly 1 troy ounce of gold but are struck in 22K alloy for durability. You’re buying 1 oz of gold — the alloy metals are added to reach the total coin weight, not to reduce gold content.
✓ Pro Tip
When comparing investment coins, focus on the actual gold content rather than the karat rating. A 22K American Gold Eagle and a 24K Canadian Maple Leaf both contain exactly 1 troy ounce of pure gold — they are equivalent investments despite different purity ratings.
The Fineness System
The fineness system expresses gold purity in parts per thousand (‰). Pure gold = 1000 fine, or written as .999, .9999, etc.
| Fineness | Percentage | Karat Equivalent | Common Use |
|---|---|---|---|
| .999 | 99.9% | ~24K | Standard bullion bars, many coins |
| .9999 | 99.99% | 24K (four nines) | Canadian Maple Leaf, premium bars |
| .99999 | 99.999% | 24K (five nines) | Specialty products |
| .9950 | 99.5% | 23.88K | Minimum investment gold standard |
| .9167 | 91.67% | 22K | American Gold Eagle |
| .750 | 75.0% | 18K | Jewelry standard |
| .585 | 58.5% | 14K | Jewelry standard |
Which system to use?
- Investment products: fineness is standard (you’ll see “.999 fine” or “9999” stamped on bars)
- Jewelry: karats are standard (you’ll see “18K”, “14ct”, etc. on hallmarked pieces)
- Both systems are used globally; context determines which you’ll encounter
Investment-Grade Gold Standards
The IRS Definition
The IRS defines investment-grade gold (eligible for gold IRAs and certain tax treatments) as:
- Gold coins: Must be at least .9950 fine (99.5% pure) AND be a legal tender coin of a recognized country
- Gold bars: Must be at least .9950 fine AND manufactured by an approved assayer, refiner, or manufacturer
Important exception: American Gold Eagles are specifically exempt from the .995 minimum requirement for IRA purposes — they’re eligible despite being .9167 fine — because they’re official US government coins.
ℹ Note
The IRS exception for American Gold Eagles is significant for IRA investors. Despite being 22K (below the normal .995 minimum), Eagles are the only sub-.995 gold product eligible for inclusion in a precious metals IRA.
LBMA Good Delivery Standards
The London Bullion Market Association (LBMA) defines standards for gold bars traded in the professional market:
- Minimum fineness: .9950 (99.5%)
- Standard bar weight: 350-430 troy ounces (~10.9-13.4 kg)
- Assay certificate: Required for each bar
- Acceptable refiners: Must be on the LBMA’s Good Delivery list
LBMA Good Delivery bars are the global standard for large institutional gold trading. When central banks and bullion banks move gold, it moves in these bars.
Reading Purity Markings on Different Products
Investment Bars
Reputable bars are stamped directly with:
- Refiner name/logo (PAMP Suisse, Valcambi, APMEX, Perth Mint, etc.)
- Weight (1 troy oz, 100g, 10 oz, etc.)
- Fineness (PAMP bars typically read “999.9” or “Au 999.9”)
- Serial number (for bars 1 oz and larger)
- Assay certificate may be included in a sealed blister pack (CertiCard)
Always buy bars that clearly display all four elements. Bars without refiner identification or fineness markings are suspect.
Bullion Coins
Official government mint coins display purity on the coin itself:
- American Gold Eagle: “1 OZ. FINE GOLD ~1/10 AGW” (actual gold weight is marked)
- Canadian Gold Maple Leaf: “FINE GOLD 1 OZ OR FIN” + “9999”
- South African Krugerrand: “FYNGOUD 1OZ FINE GOLD”
- Austrian Philharmonic: “1 UNZE GOLD” (1 ounce gold)
For coins, purity is implicit from the design — a recognized sovereign coin from an established mint is a guarantee of purity. The design itself is the authentication.
Jewelry
Jewelry hallmarks are tiny stamps, often inside rings or on clasps:
- US standard: “14K”, “18K”, “750”, “585” (fineness equivalent)
- UK standard: Assay office mark (anchor=Birmingham, leopard=London), date letter, fineness mark (750, 585, 375)
- International: ISO fineness marks (750=18K, 585=14K, 375=9K)
Jewelry marks are much smaller and may require magnification to read. A jeweler’s loupe (10x magnification) reveals marks invisible to the naked eye.
The “Nines” Hierarchy
Premium gold products compete on the number of “nines” in their purity:
Three nines (.999 = 99.9%): This was long the standard for investment gold. Many major bars (Perth Mint cast bars, generic silver bars) are .999 fine. A trace 0.1% impurity remains (typically silver or copper).
Four nines (.9999 = 99.99%): The Canadian Gold Maple Leaf, introduced in 1979, was the world’s first .9999 fine gold coin. This became the gold standard (literally) for premium investment coins. Today, .9999 fine is standard for:
- Canadian Gold Maple Leaf
- American Gold Buffalo
- Perth Mint Gold Kangaroo
- Most premium PAMP, Valcambi, and Credit Suisse bars
Five nines (.99999 = 99.999%): Some specialty products claim five-nines purity. The Royal Canadian Mint has produced limited .99999 coins. From an investment standpoint, the difference between .9999 and .99999 is negligible for bullion purposes.
What’s the practical difference? For investment purposes, .999 fine and .9999 fine gold contain nearly identical value. A 1 oz .9999 coin contains 0.1% more gold than a .999 coin — worth roughly $4 at a $4,200 spot price. The premium you pay for .9999 products typically exceeds this marginal gold content difference.
The value of .9999 certification lies primarily in:
- Ease of assaying — easier to verify
- Prestige/recognition — Maple Leafs command premium buyback prices
- Consistency — sophisticated refining processes ensure uniformity
The Canadian Gold Maple Leaf, introduced in 1979, was the world’s first .9999 fine gold coin. This four-nines standard became the global benchmark for premium investment gold.
Calculating Gold Content Value
When buying or selling gold products, you can calculate the pure gold value:
Formula: Weight (troy oz) × Fineness × Spot price = Gold value
Example 1 — American Gold Eagle:
- Weight: 1.0909 troy oz total (but contains exactly 1 troy oz of gold in the 22K alloy)
- Gold fineness: .9167
- Spot price: $4,200
- Gold value: 1.0909 × .9167 × $4,200 = $4,200 (by design — it contains exactly 1 oz gold)
Example 2 — 10 gram bar at .999 fine:
- Weight: 10 grams = 0.3215 troy oz
- Fineness: .999
- Spot price: $4,200
- Gold value: 0.3215 × .999 × $4,200 = $1,348.95
Example 3 — 18K gold bracelet, 8 grams:
- Weight: 8 grams = 0.2572 troy oz
- Fineness: .750
- Spot price: $4,200
- Gold value: 0.2572 × .750 × $4,200 = $810.18
This explains why scrap gold dealers pay so much less for jewelry — you’re only getting value for the actual gold content, not the total weight.
⚠ Warning
When selling gold jewelry for scrap, dealers pay based on gold content, not total weight. A 10-gram 14K bracelet contains only 5.83 grams of actual gold. Understand this calculation before selling to avoid feeling shortchanged by legitimate offers.
When selling 14K jewelry for scrap, only 58.3% of the total weight is actual gold -- the remaining 41.7% is base metal with minimal resale value. Always calculate the gold content before accepting an offer.
Purity Testing Methods
If you want to verify purity beyond reading stamps:
Acid testing — drops of nitric acid on a stone streak reveal purity based on reaction Electronic testing — electrical resistance measurements indicate approximate purity XRF (X-ray fluorescence) — non-destructive, most accurate for surface analysis; shows full elemental composition Fire assay — melting and cupellation; destructive but most accurate Ultrasound — used for large bars to detect internal composition
For typical investor purchases from reputable dealers, verifying the weight and physical dimensions (plus visual inspection) is sufficient. Purity testing is most relevant when buying from unknown sources.