Gold Karat Purity Guide for Jewelry Makers

Every gram of gold in your studio has a purity level, and that purity determines its cost, its workability, and whether your COGS calculations mean anything at all. Yet "gold" gets treated as a single line item in too many inventory systems — and too many jewelers' heads.

This guide covers everything a bench jeweler or studio owner needs to know about gold karat purity: what the numbers actually mean, how they affect your material costs at current spot prices, and why getting purity tracking right is foundational to running a profitable shop.

What karat actually means

Karat is a measure of gold purity, not weight. It tells you how much of an alloy is pure gold, expressed on a 24-part scale.

• 24K = 24 out of 24 parts are pure gold (99.9% gold)
• 18K = 18 out of 24 parts are pure gold (75% gold)
• 14K = 14 out of 24 parts are pure gold (58.3% gold)
• 10K = 10 out of 24 parts are pure gold (41.7% gold)

The remaining parts are alloyed metals — silver, copper, palladium, nickel, zinc — chosen to give the metal its color, hardness, and working properties. A 14K ring isn't "lesser gold." It's an engineered alloy where 14 of every 24 parts are pure gold, and the other 10 parts are doing real work: adding strength, shifting color, improving castability.

Karat vs. carat vs. karat weight

These three terms cause more confusion than anything else in the trade. Here's the distinction:

• Karat (K or kt) — gold purity. 14K means 58.3% pure gold. Used exclusively for gold alloys.
• Carat (ct) — gemstone weight. 1 carat = 0.2 grams. A 1.5ct diamond weighs 0.3g. Has nothing to do with gold.
• Karat weight — occasionally used in older trade references to describe the weight of gold at a specific purity. Not a standard modern term and best avoided to prevent confusion.

In the US trade, "karat" with a K is always gold purity. "Carat" with a C is always gemstone weight. If your raw materials tracking system conflates these, you've got a data integrity problem waiting to happen.

The karat purity chart

This table covers every karat grade you're likely to encounter at the bench or in your inventory. The millesimal fineness is the international standard — a three-digit number representing parts per thousand of pure gold.

Alloy metals: what they are and why they matter

Gold purity tells you how much of the alloy is gold. The alloy composition tells you everything else: color, hardness, melting point, workability at the bench, and whether the piece will hold up to daily wear.

Yellow gold

Gold + silver + copper in varying ratios. The classic alloy. Higher-karat yellow gold (18K+) has a richer, deeper hue because there's more actual gold present. 10K yellow can appear slightly greenish or pale depending on the alloy balance.

White gold

Gold + palladium (or nickel) + zinc + sometimes silver. Almost always rhodium-plated for that bright white finish. Nickel-based white gold is cheaper but causes allergic reactions in roughly 10–15% of wearers. Palladium-based alloys cost more but are hypoallergenic and increasingly preferred. The rhodium plating wears off over time — customers need to know this at point of sale.

Rose gold

Gold + a higher ratio of copper (+ a small amount of silver). The copper gives it the pink warmth. 14K rose gold has a more pronounced pink than 18K rose because the copper percentage is higher. Rose gold does not get rhodium plated — its color is intrinsic to the alloy.

Cost per gram at each purity level

This is where purity directly hits your bottom line. The formula is straightforward, and every jeweler should know it cold.

The formula

1. Start with the spot price of pure gold per troy ounce (as of April 2026: ~$5,050/oz)
2. Divide by 31.1035 to get the price per gram of pure gold: $5,050 ÷ 31.1035 = $162.37/g
3. Multiply by the purity percentage for your karat

The difference between 10K and 18K gold is $54.07 per gram. On a 5g ring, that's $270 in material cost difference — before waste factor, labor, or findings. This is exactly why accurate COGS calculation requires knowing the purity of every gram in your inventory.

Why purity tracking matters for inventory management

Here's the reality most inventory systems ignore: a shop with 500g of "gold" doesn't have 500g of gold. It has some combination of 14K yellow, 14K white, 14K rose, 18K yellow, 18K rose, and maybe 10K yellow — each with a different cost per gram, different working properties, and different end-use constraints.

You can't substitute 14K for 18K in a customer order. You can't mix 14K yellow scrap with 18K yellow scrap without devaluing the higher-purity metal. These are fundamentally different materials that happen to share the word "gold."

What purity tracking enables

• Accurate inventory valuation. 100g of 18K gold is worth $12,178 at current spot. 100g of 10K is worth $6,771. If your system tracks both as "gold," your balance sheet is wrong by thousands.
• Correct COGS per piece. A ring's material cost starts with grams × cost-per-gram-at-purity. Wrong purity data means wrong COGS, which means wrong margins, which means wrong pricing.
• Meaningful reorder triggers. Running low on 14K yellow wire is a different purchasing decision than running low on 18K rose sheet. A single "gold" inventory line can't tell you which one needs reordering.
• Scrap management. Bench scrap should be separated by purity and alloy color. Mixed scrap gets refined at the lowest common purity — meaning you lose money on every gram of higher-karat metal in the mix.

Hallmarking and legal requirements

Karat purity isn't just a quality descriptor — it's a legally regulated claim in most markets.

United States

The FTC's Jewelry Guides require that any item marketed as "gold" must be at least 10K. Karat fineness must be marked on the piece, and it must be accompanied by a registered trademark or manufacturer's mark. A piece marked "14K" must contain at least 13.5K gold to account for manufacturing tolerance (a 0.5K tolerance is permitted). Misrepresenting karat is a violation of FTC trade practice rules.

United Kingdom

The UK has one of the strictest hallmarking systems in the world. The Hallmarking Act 1973 requires that any item described as gold must be independently assayed and hallmarked at one of four assay offices (London, Birmingham, Sheffield, Edinburgh). Permitted gold standards are 9K (375), 14K (585), 18K (750), and 22K (916). Selling unhallmarked gold above 1g is a criminal offense.

International

Standards vary significantly. The Vienna Convention on the Control and Marking of Articles of Precious Metals provides a framework for international hallmark recognition among member states. If you sell internationally, you need to know the minimum purity standards for each market — what's legal in one country may not be in another.

Common mistakes jewelers make with purity

After years of watching jewelers manage (and mismanage) their gold inventory, these are the errors that show up again and again:

1. Not tracking alloy color separately from purity

Your system says you have 200g of 14K gold. But how much of that is yellow vs. white vs. rose? These have different alloy compositions, different costs (white gold with palladium costs more), and are not interchangeable in production. Purity and alloy color are two independent attributes — track them both.

2. Mixing scrap from different purities

That scrap jar on your bench is costing you money. If you're tossing 18K filings in with 14K clippings, the entire batch gets valued at the lower purity when it goes to the refiner. Separate scrap containers for each purity and alloy color. Label them clearly. Train everyone at the bench to sort correctly.

3. Using the wrong spot price calculation

The spot price of gold is for pure gold — 24K, 999 fine. When you're calculating material cost for a 14K piece, you have to multiply by 0.583, not use the spot price directly. Getting this wrong inflates your apparent material cost by 40–70%, which cascades into bad pricing and distorted margins. The COGS formula walks through this step by step.

4. Not accounting for purity when calculating waste factor costs

A 10% waste factor on 18K gold costs you $12.18 per gram wasted. The same 10% waste on 10K gold costs $6.77 per gram. If your waste factor costing doesn't adjust for purity, you're undercosting high-karat work and overcosting lower-karat pieces. Both lead to bad pricing decisions.

5. Assuming all suppliers' karat claims are accurate

Trust, but verify. Testing incoming material with an XRF analyzer or acid test kit protects you from receiving 13.8K metal that's marked as 14K. Even small deviations compound across hundreds of grams. If you don't own testing equipment, build a relationship with a refiner or assay office that can verify purity on incoming stock.

Putting it together

Gold karat purity is one of those foundational concepts that touches everything else in a jewelry business: pricing, cost accounting, inventory management, purchasing, legal compliance, and customer communication. Getting it right means treating every karat-and-color combination as its own distinct material with its own cost, its own inventory count, and its own line in your BOM.

The math isn't hard. The discipline to track it consistently is what separates shops that know their margins from shops that guess at them.