Gold Karat Calculator - Purity & Fine Gold Weight | 1Dollars

Free Gold Karat Calculator

Convert gold karat into purity percentage and millesimal fineness, then calculate the fine-gold and alloy-metal content of an item. Choose a common hallmark grade or enter any custom karat from 0.01K to 24K.

Gold Karat to Purity Calculator

Choose a hallmark grade and calculation basis. Add weight to find how much fine gold and other alloy metal the item contains.

Common marks and exact karat fractions can differ slightly.

Gold Purity Used91.6%
Selected gold grade22K / 916
Millesimal fineness used916
Exact K ÷ 24 purity91.6667%
Difference from exact fraction-0.0667 pp
Total alloy weight10 g
Fine-gold content9.16 g
Other alloy-metal content0.84 g
Fine gold in troy ounces0.294501 ozt

Using the selected 916 hallmark fineness. Exact 22K ÷ 24 is shown separately for comparison.

This is a mathematical converter, not an assay or hallmark verification. Item weight may include solder, stones, enamel or non-gold components unless they are removed.

Reviewed on 15 July 2026 using BIS gold fineness grades, World Gold Council purity information, NIST troy-weight conversions and current U.S. FTC jewelry guidance.

Gold karat measures how many of 24 parts are gold. This calculator converts karat to an exact mathematical percentage, compares it with a common millesimal fineness mark and uses your chosen basis to split total item weight into fine gold and other alloy metal.

Quick answer: Select a common gold grade or enter custom karat, choose marked fineness or exact K ÷ 24, add the item's net weight and calculate. Use the marked-fineness basis when you specifically want a 916, 750 or 585 calculation.

How the Gold Karat Calculator Works

The karat system divides a gold alloy into 24 theoretical parts. Pure gold is 24K, while 18K represents 18 parts gold out of 24. Millesimal fineness expresses gold content as parts per thousand, such as 750 for 75.0% gold.

Exact purity percentage = gold karat ÷ 24 × 100
Marked purity percentage = millesimal fineness ÷ 10
Fine-gold weight = total alloy weight × purity percentage ÷ 100
Other alloy weight = total alloy weight − fine-gold weight

Exact Karat vs Marked Fineness

Exact karat arithmetic and a marketed or hallmarked fineness are not always identical. For example, exact 14K is 14 ÷ 24 = 58.3333%, while the widely used 585 mark represents 58.5%. Exact 22K is 91.6667%, while 916 represents 91.6%.

The World Gold Council notes that 14K is strictly 583.333 parts per thousand, although many manufacturers use 585. BIS laboratory scope information lists grades including 375, 585, 750, 833, 916, 958, 995 and 999. Choose the basis that matches the mark, assay or contract you are evaluating.

Gold gradeExact K ÷ 24Common markMarked purity
24K100%99999.9%
23K95.8333%95895.8%
22K91.6667%91691.6%
21K87.5%87587.5%
20K83.3333%83383.3%
18K75%75075%
14K58.3333%58558.5%
10K41.6667%41741.7%
9K37.5%37537.5%

These are calculation references, not proof that an individual item meets its mark. Permitted tolerances, solder allowances and labeling rules depend on the applicable jurisdiction and product.

Worked 22K Gold Example

Suppose a jewelry item weighs 10 grams and is marked 22K / 916. Using the marked-fineness basis:

  • Purity used = 916 ÷ 10 = 91.6%
  • Fine gold = 10 g × 91.6% = 9.16 g
  • Other alloy metal = 10 g − 9.16 g = 0.84 g

Using exact 22 ÷ 24 instead would produce 91.6667% purity and approximately 9.166667 grams of fine gold. The calculator shows the percentage-point difference so you can see which convention was applied.

What Fine-Gold and Alloy Weight Mean

Fine-gold contentThe mathematical weight of gold implied by the selected purity. It is not the item's total gross weight.
Other alloy metalThe remaining theoretical weight, which may include silver, copper, zinc or other materials.
Millesimal finenessGold parts per thousand. A 750 mark means 750 parts gold per 1,000 parts alloy.
Percentage pointsThe arithmetic difference between the purity used and exact K ÷ 24, not a percentage change.

Karat, Carat and Fineness

“Karat” and the symbol K are commonly used for gold purity in North America. “Carat” is also used for gold fineness in other markets. Do not confuse gold carat with the carat used as a unit of gemstone mass. Millesimal fineness avoids the spelling issue by stating gold parts per thousand.

Supported Gold Weight Units

The calculator accepts grams, kilograms, troy ounces, tola, pennyweight and grains. It normalizes weight to grams before calculating fine-gold content. One troy ounce equals 31.1034768 grams, and one pennyweight equals one-twentieth of a troy ounce.

Hallmarks, Assays and Item Weight

A stamped karat or fineness mark is an input, not a laboratory result. Wear, repairs, solder, mixed components, hollow sections, stones and counterfeit marks can affect actual gold content. Use a qualified assay or appraisal when a precise commercial or legal determination is required.

Use net metal weight: gemstones, enamel, watch movements, steel springs and other non-gold parts can overstate calculated fine-gold content when included in the entered weight.

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Frequently Asked Questions

How do I convert gold karat to purity percentage?
Divide the karat number by 24 and multiply by 100. For example, exact 18K purity is 18 ÷ 24 × 100 = 75%.
What percentage of gold is 22K?
Exact 22K arithmetic is 91.6667%. A common 916 fineness mark represents 91.6%, so select the calculation basis that matches your mark or purpose.
What percentage of gold is 14K?
Exact 14K arithmetic is 58.3333%. The common 585 mark represents 58.5% gold.
Is 24K always exactly 100% gold?
24K describes the highest karat grade, but real products may be marked by measured fineness such as 999 or 999.9 rather than mathematical 100%. Use the stated fineness when that is the relevant specification.
What does 916 mean on gold?
916 means 916 parts gold per thousand parts alloy, equal to 91.6% gold. It is commonly associated with 22K gold.
Why does 585 differ from exact 14K?
Exact 14 ÷ 24 equals 58.3333%, or 583.333 fineness. Many manufacturers use the common 585 specification, which equals 58.5%.
How do I calculate fine gold in jewelry?
Multiply the item's net gold-alloy weight by the selected purity percentage. Ten grams at 75% purity contains a theoretical 7.5 grams of fine gold.
Can I enter a custom gold karat?
Yes. Enter any value above 0K and no more than 24K. Custom karat uses the exact K ÷ 24 formula because no separate hallmark fineness is supplied.
Are karat and carat the same for gold?
Both spellings are used for gold purity in different markets. For gemstones, carat instead refers to mass, so context matters.
Does this calculator verify a gold hallmark?
No. It converts the selected grade mathematically. Only appropriate hallmark verification, testing or assay can establish an item's actual fineness.

Reference Sources

Disclaimer: This calculator and guide provide general mathematical estimates, not a hallmark verification, assay, appraisal, live gold price, buyer quote, investment recommendation or legal determination. Verify actual weight and fineness independently before a transaction.