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Karat Purity Converter

Everyday

Convert gold purity between karat (24k, 22k, 18k, 14k), percentage fineness, and millesimal fineness (750, 916, 999) — for jewellery buyers and investors.

Reviewed by the thecalcu.com team · Last updated July 28, 2026

From
To
All conversionsfor 1 Karat (K, out of 24)
Karat (K, out of 24)1
Purity (%)4.1666667
Millesimal Fineness (per 1000)41.666667
Purity (fraction, 0-1)0.041666667

What is a Karat Purity?

A Karat Purity Converter translates gold purity between the three systems commonly seen on jewellery, hallmarks, and gold market listings: karat (the familiar 24k/22k/18k scale), percentage purity, and millesimal fineness (the three-digit hallmark number like 916 or 750). All three describe exactly the same thing, what fraction of the metal's weight is pure gold, just expressed with different scales and conventions.

This is especially relevant in India, where the Bureau of Indian Standards (BIS) hallmarking scheme uses millesimal fineness numbers (916, 750, 999) on jewellery, while sellers and buyers commonly discuss purity using the karat scale (22k, 18k, 24k). Being able to move fluidly between the two avoids confusion when comparing jewellery from different sellers or verifying a hallmark's claimed purity.

Why Use a Karat Purity Converter?

Gold jewellery, coins, and bars are labelled with different purity systems depending on the seller, country, and hallmarking standard, a US retailer might advertise "14k gold" while an Indian jeweller's hallmark reads "585" or "916," and without converting between systems, it's not obvious whether two pieces have comparable purity. Manually calculating karat-to-percentage or karat-to-millesimal requires a simple but easy-to-get-wrong division.

Two concrete situations this solves: converting a jewellery listing's karat rating into the millesimal fineness hallmark number to verify it matches the physical hallmark stamped on the piece, and comparing a US 14k gold ring's purity percentage against an Indian 22k piece to understand the actual gold content difference.

Who Should Use This Converter?

  • Jewellery buyers in India verifying that a piece's karat claim matches its BIS hallmark millesimal fineness number (916, 750, 999).
  • Gold investors comparing purity across karat, percentage, and millesimal fineness when evaluating coins, bars, or jewellery as an investment.
  • Jewellers and goldsmiths converting between purity systems when sourcing gold alloys or verifying supplier certifications.
  • International shoppers comparing gold jewellery purity between US (karat-labelled) and Indian (hallmark-labelled) retailers.
  • Students and hobbyists learning how gold purity grading systems relate to one another mathematically.

What Insights Does the Karat Purity Converter Give You?

Converting to Purity (%) gives you the most intuitive, universally understood purity figure, useful for quick comparisons regardless of which labelling system a seller uses. Converting to Millesimal Fineness (per 1000) gives you the exact number that should appear on a BIS hallmark or international fineness stamp, letting you cross-check a jewellery piece's physical markings against its advertised karat rating.

Because these three systems are all linearly related (they're just different scales measuring the same purity fraction), the converted values are exact, there's no approximation or rounding uncertainty involved, unlike some of the cross-standard comparisons found elsewhere on this platform.

How to use this Karat Purity calculator

  1. Select your starting unit from the From dropdown, Karat, Purity (%), or Millesimal Fineness.
  2. Enter your value, such as 22 for 22 karat gold.
  3. Select your target unit from the To dropdown, such as Millesimal Fineness (per 1000).
  4. Read the converted result, which updates instantly.
  5. Use the swap (⇅) button to convert a hallmark number or percentage back into its karat equivalent.
  6. Compare the result against the physical hallmark stamped on your jewellery to verify its claimed purity.

Formula & Methodology

All three purity systems are directly proportional to the same underlying pure-gold fraction (0 to 1), making this a fully linear conversion:

Percentage (%) = (Karat ÷ 24) × 100  |  Millesimal Fineness = (Karat ÷ 24) × 1000

Worked example: Converting 18 karat gold, Purity fraction = 18 ÷ 24 = 0.75. As a percentage: 0.75 × 100 = 75%. As millesimal fineness: 0.75 × 1000 = 750, exactly matching the "750" hallmark commonly stamped on 18 karat gold jewellery.

Frequently Asked Questions

22k (22 karat) gold means 22 parts out of 24 are pure gold, giving a purity of approximately 91.7%, the remaining 2 parts are other metals like silver, copper, or zinc added for durability. Pure gold, at 24k, is too soft for most jewellery, which is why 22k and 18k are the most common purities used in Indian gold jewellery.
Percentage purity = (Karat ÷ 24) × 100, since the karat scale is defined out of 24 parts representing pure gold. For example, 18 karat gold converts to (18 ÷ 24) × 100 = 75% purity.
The 916 hallmark is the millesimal fineness marking for 22 karat gold, meaning 916 parts per 1000 are pure gold (91.6%), it's the standard purity marking used by the Bureau of Indian Standards (BIS) hallmarking scheme. Similarly, an 750 hallmark indicates 18 karat gold (75% pure), and 999 indicates 24 karat (99.9% pure).
Select Karat (K, out of 24) as your From unit, enter the karat value, and select Millesimal Fineness (per 1000) as your To unit. For example, 22 karat converts to a millesimal fineness of approximately 917, close to the standard BIS 916 hallmark (small rounding differences exist between the exact mathematical conversion and the standardised hallmark numbers).
Karat (with a K) measures gold purity out of 24 parts, while carat (with a C) measures gemstone or diamond weight, where 1 carat equals 200 milligrams, the two words sound identical but measure completely different things. Use this converter for gold purity and the [Diamond Carat to Grams Converter](/carat-to-grams-converter/) for gemstone weight.
22 karat (916 hallmark) is the most popular choice for Indian gold jewellery, balancing high purity with enough durability for daily wear, while 18 karat (750 hallmark) is increasingly popular for diamond-studded and Western-style jewellery due to its greater hardness and scratch resistance. 24 karat gold is too soft for most jewellery designs and is typically reserved for coins, bars, and investment purposes.
Compare the millesimal fineness number stamped on the jewellery (like 916, 750, or 999) against the value this converter calculates for the karat purity claimed by the seller, a mismatch may indicate mislabelled or under-karated gold. For legally verified purity in India, always check for the BIS hallmark along with the jeweller's registration number and the Hallmark Unique Identification (HUID) number.
14 karat gold (about 58.3% pure, 585 millesimal fineness) is common in US and Western jewellery for its balance of durability, lower cost, and gold appearance, but is less commonly used in India, where 22k and 18k dominate the market. This converter shows the exact percentage and millesimal fineness for 14k alongside all other standard karat values.
Not necessarily, higher karat gold is purer but softer and more prone to scratching and bending, so 24 karat isn't always the 'best' choice for jewellery meant for daily wear, even though it commands a higher price for its gold content. The right karat depends on the intended use: 24k for investment bars/coins, 22k or 18k for wearable jewellery.
Gold purity (karat) determines what fraction of the jewellery's weight is actual gold, while total weight (measured in grams) determines the overall gold content, jewellery price is typically calculated using both, as (weight × purity fraction × gold rate per gram) plus making charges. This converter calculates purity only; multiply the resulting fraction by the jewellery's weight to estimate actual gold content.
Also known as
24k to percent22k gold puritykarat to millesimal fineness916 gold purity750 gold hallmarkgold purity calculator