Convert a precious metal’s karat, purity percentage, decimal purity, or millesimal fineness into the other formats. Add an item weight to estimate its pure-metal content, then enter a pure-metal price if you also want an estimated intrinsic value.
Last Updated: July 21, 2026
Metal Purity & Fineness Calculator
Convert purity formats and calculate fine-metal content.
Conversion Results
Karat is primarily a gold-purity scale. For other metals, the karat figure is a mathematical equivalent.
How to Use This Metal Purity Calculator
- Select the metal. This labels your results but does not change the conversion formula.
- Choose the purity format printed on your item or shown in an assay result.
- Enter the purity value. For example, enter 18 for 18K gold, 925 for sterling silver, or 95 for 95% platinum.
- Add the item’s gross weight and choose its unit if you want pure-metal weight.
- Optionally enter the current price of pure metal per gram to estimate intrinsic metal value.
- Select Calculate and review all four equivalent purity formats.
The preset buttons provide fast examples. They change the input format to fineness, insert the selected mark, and recalculate. They do not verify whether a stamp is genuine.
Metal Purity, Fineness, and Karat Explained
Purity describes the share of a metal item made from the named precious metal. Jewelry and industrial products often contain an alloy because pure precious metals may be too soft, costly, or unsuitable for the intended use. The remaining portion may contain copper, silver, nickel, zinc, cobalt, ruthenium, or another metal.
Millesimal fineness expresses purity in parts per thousand. A 925 silver item contains a nominal 925 parts silver per 1,000 parts of alloy, equal to 92.5%. A 950 platinum item represents 95% platinum. A 750 gold item represents 75% gold.
Karat, written K or kt, divides gold purity into 24 parts. The U.S. Federal Trade Commission explains that 18K gold contains 18 parts gold and six parts other metal. Pure gold is described as 24K. Karat is different from carat, a unit of gemstone mass.
Decimal purity expresses the same ratio from 0 to 1. For example, 0.925 equals 92.5%, 925 fineness, and a mathematical karat equivalent of 22.2K.
Purity Conversion Formulas
Fineness = purity decimal × 1,000
Karat equivalent = purity decimal × 24
Pure-metal weight = gross weight × purity decimal
Intrinsic metal value = pure weight in grams × pure-metal price per gram
The converter calculates from the precise input you enter. It does not force a value such as 916 into exactly 22K. This distinction matters because 916 fineness equals 21.984K, while 22K by the exact 24-part formula equals 916.6667 fineness. Commercial marks often use accepted rounded grades.
Worked Example: 10 Grams of 22K Gold
Assume a gold item weighs 10 grams and its stated purity is 22K.
- Purity decimal = 22 ÷ 24 = 0.9166667
- Purity percentage = 0.9166667 × 100 = 91.6667%
- Millesimal fineness = 0.9166667 × 1,000 = 916.667
- Pure gold weight = 10 g × 0.9166667 = 9.1667 g
- Other alloy weight = 10 g − 9.1667 g = 0.8333 g
If pure gold costs 100 currency units per gram, the estimated intrinsic gold value is 9.1667 × 100, or 916.67 currency units. A buyer’s offer may be lower after assay, refining, handling, and dealer deductions. Finished jewelry may sell above intrinsic value due to labor, design, tax, brand, or gemstones.
Common Gold, Silver, and Platinum Fineness Marks
| Mark or grade | Purity | Karat equivalent | Typical context |
|---|---|---|---|
| 999 | 99.9% | 23.976K | Fine gold or fine silver bullion |
| 950 | 95% | 22.8K equivalent | Common platinum alloy grade |
| 925 | 92.5% | 22.2K equivalent | Sterling silver |
| 916 | 91.6% | 21.984K | Common rounded mark associated with 22K gold |
| 875 | 87.5% | 21K | 21K gold |
| 750 | 75% | 18K | 18K gold |
| 585 | 58.5% | 14.04K | Common rounded 14K gold mark |
| 417 | 41.7% | 10.008K | Common rounded 10K gold mark |
| 375 | 37.5% | 9K | 9K gold |
These descriptions are general references, not an authentication guide. Hallmark formats, permitted tolerances, legal minimums, and mandatory marking rules vary by country and product type.
Fineness vs Hallmark: What Is the Difference?
Fineness is a numerical statement of precious-metal content. A hallmark is an official mark or group of marks applied under a recognized hallmarking system. India’s Bureau of Indian Standards describes hallmarking as the accurate determination and official recording of the proportionate precious-metal content. A complete hallmark may include more than a three-digit purity number.
A lone “750” or “925” stamp should not be treated as conclusive proof. Stamps may be counterfeit, altered, incorrectly applied, or refer only to a plated layer. High-value transactions need inspection by a qualified jeweler, assay office, refiner, or testing laboratory.
Why Calculated Value May Differ From a Buyer’s Offer
This tool estimates contained metal from stated purity. It does not estimate a guaranteed cash offer. Differences often result from:
- Assay results that differ from the stamped grade
- Solder, stones, clasps, springs, and non-metal components included in gross weight
- Gold plating, gold filling, vermeil, or bonded layers over base metal
- Refining loss, treatment fees, shipping, and minimum charges
- Dealer payout percentages and bid-ask spreads
- Collectible, artistic, historical, or brand value above melt value
- Taxes, making charges, and local market premiums
For a selling estimate, calculate pure content first, then use a metal dealer payout percentage calculator to compare an offer with theoretical melt value.
Accuracy and Rounding
The result is only as accurate as your input. Use a calibrated scale and keep enough decimal places for small items. Troy ounces and ordinary ounces are different. One troy ounce equals 31.1034768 grams, while one avoirdupois ounce equals 28.349523125 grams.
The calculator preserves the input ratio internally and rounds only the displayed result. A stamped commercial grade may use a conventional rounded value. For example, exact 14K purity is 14 ÷ 24, or 58.3333%, while the widely seen 585 mark means 58.5%. Enter the format printed on your item rather than assuming the two values are numerically identical.
Choosing the Correct Input Format
Use karat when a gold item is marked with a value such as 9K, 10K, 14K, 18K, 21K, or 22K. Use fineness when you see a three-digit number such as 375, 585, 750, 916, 925, 950, or 999. Use percentage when a laboratory report or product specification states purity with a percent sign. Use decimal purity when your source supplies a ratio such as 0.9995.
Do not enter a three-digit fineness mark in karat mode. For example, 750 belongs in fineness mode, not karat mode. The calculator blocks karat values above 24 to prevent this error. Likewise, enter 92.5 rather than 0.925 in percentage mode. When you know only a marketing description such as “fine,” “sterling,” or “high purity,” find the actual stated grade before calculating.
If an item contains stones, enamel, internal mechanisms, or detachable fittings, gross weight may overstate its precious-metal weight. Remove only components that you can separate safely and lawfully. Otherwise, ask a qualified professional to estimate net metal weight.
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Frequently Asked Questions
What does fineness mean in precious metals?
Fineness states the proportion of pure precious metal in parts per thousand. A 750 mark means 750 parts of the named metal per 1,000 parts of alloy, equal to 75% purity.
How do I convert fineness to percentage?
Divide fineness by 10. For example, 925 fineness divided by 10 equals 92.5% purity.
How do I convert karat to fineness?
Divide karat by 24, then multiply by 1,000. Exact 18K equals 750 fineness. Exact 22K equals about 916.667 fineness.
Is 916 gold the same as 22K gold?
They are commonly treated as the same commercial grade. Numerically, 916 fineness is 91.6% or 21.984K, while exact 22K equals 91.6667% or 916.667 fineness.
What does 925 mean on silver?
A 925 mark represents 92.5% silver by nominal metal content. It is commonly associated with sterling silver.
Does a purity stamp prove an item is genuine?
No. A stamp alone does not prove authenticity or actual composition. Use professional testing or a recognized assay service for a high-value purchase or sale.
Can I use karat for silver or platinum?
Karat is mainly used for gold. The calculator displays a mathematical 24-part equivalent for other metals, but fineness or percentage is normally clearer for silver, platinum, and palladium.
How is pure-metal weight calculated?
Multiply gross item weight by the purity decimal. A 20 gram item at 925 fineness contains an estimated 18.5 grams of the named metal before adjustments for non-metal parts.
Does this calculator verify a hallmark or assay?
No. It converts entered numbers and estimates contained metal. It does not inspect, authenticate, assay, or certify an item.