Calculator Tools
Gold Karat Purity Calculator
Convert between gold karat, fineness, and mass percent in your browser. Includes a scrap gold calculator with weight, spot price, and refiner payout.
Common karat presets
Click any preset to load that karat and its standard hallmark equivalent into the calculator.
Enter purity in any unit
Parts gold per 24. 24K is pure; 18K is 18/24 of the alloy by mass.
Millesimal fineness. European hallmarks stamp this value directly: 585 = 14K, 750 = 18K, 999 = pure.
The grams of gold in 100 g of alloy. 18K = 75% gold by mass.
Pure gold mass and scrap value
Enter the item weight and an optional spot price to estimate the melt value and a refiner payout. Spot price is yours to type in (the tool never fetches market data).
Troy ounce and pennyweight are the trade standards for gold; avoirdupois ounce is the unit on most kitchen scales.
Type the current spot price from your preferred source. The calculator does not call any external service.
Refiners and pawn shops typically quote a percentage of spot (commonly 70 to 90% for scrap gold). Set to 100 for the raw melt value.
Pure gold mass
7.5 g
0.24113 ozt
4.8226 dwt
Item weight times purity fraction.
Alloy weight (grams)
10 g
Normalized to grams for the math.
Price per gram of alloy
$57.8713
Effective per-gram price given the purity.
Melt value (100% of spot)
$578.71
Pure gold mass times spot price per gram.
Estimated payout at 80%
$462.97
Melt value times the chosen payout percentage.
Equation
value = weight_g * (karat/24) * spot_per_g
payout = value * payout%/100
What the calculator is computing under the hood.
Karat, fineness, and hallmark reference
Karat and fineness are exact mathematical equivalents; the hallmark column is the stamped value used in the trade, which is rounded by convention.
| Karat | Fineness (exact) | Mass percent | Common hallmark | Where you see it |
|---|---|---|---|---|
| 8K | 333.33 | 33.333% | 333 | Common in Germany |
| 9K | 375 | 37.5% | 375 | UK, Ireland |
| 10K | 416.67 | 41.667% | 417 | Common in the US |
| 12K | 500 | 50% | 500 | Rare; half pure |
| 14K | 583.33 | 58.333% | 585 | Most common US karat |
| 15K | 625 | 62.5% | 625 | Antique British |
| 18K | 750 | 75% | 750 | Fine jewelry standard |
| 20K | 833.33 | 83.333% | 833 | Older Asian gold |
| 21K | 875 | 87.5% | 875 | Middle East market |
| 22K | 916.67 | 91.667% | 916 | Indian wedding gold |
| 23K | 958.33 | 95.833% | 958 | Britannia silver karat equivalent |
| 24K | 1,000 | 100% | 999 | Pure gold bullion (24K) |
How karat and fineness relate
- Karat is a fraction of 24 parts. Pure gold is 24K; a 14K alloy contains 14 parts gold and 10 parts other metals (copper, silver, palladium, zinc, nickel).
- Fineness is parts per 1000. Multiply the karat fraction by 1000 to get the fineness used on European and modern jewelry hallmarks.
- Hallmark vs math 14K stamps as 585 (instead of 583.33) and 9K stamps as 375 (exact). The hallmark value is what assay offices accept; the underlying alloy is whichever value the jeweler actually mixed.
- Karat is not carat. Spelled the same in some markets, but a metric carat is 0.2 g of gem weight and is unrelated to gold purity. This calculator works in gold karat only.
Scrap value notes
- Spot price is the live market quote per troy ounce. The calculator divides through by 31.1034768 g/ozt to compute a per-gram price.
- Melt value is the theoretical maximum: pure gold mass multiplied by the spot per-gram price.
- Payout percent lets you model what a refiner or pawn shop will actually pay. Common ranges are 70 to 90% of melt for scrap; coins and recognized bullion typically pay closer to spot.
- Solder and stones are not subtracted automatically. Subtract the estimated non-gold weight (gemstones, clasps, prongs) from the item weight before using this tool if you want a tighter figure.
- This is a planning estimate, not an appraisal. Verify the karat stamp with a jeweler or X-ray fluorescence test before selling anything valuable.
How to use
- Pick a karat preset (such as 14K, 18K, or 22K) or type a custom value in karat, fineness, or percent. The other two fields update automatically.
- Enter the item weight and choose grams, troy ounces, pennyweight, or avoirdupois ounces. Use the trade-standard troy ounce or pennyweight for gold; avoirdupois ounce is the unit on most kitchen scales.
- Optionally enter a spot price with your preferred currency symbol and choose whether the price is per troy ounce, per gram, or per pennyweight. The calculator handles the conversion.
- Adjust the refiner payout percent to model what a buyer will actually pay (commonly 70 to 90% of melt for scrap). Set to 100 for the raw melt value.
- Read the pure gold mass, alloy melt value, and estimated payout. Click Copy summary to save the full breakdown as plain text for your records.
About this tool
Gold Karat Purity Calculator converts gold purity between the three units the trade actually uses (karat, millesimal fineness, and mass percent) and then lets you apply that purity to a real-world weight and spot price to estimate scrap or melt value. Enter a karat (8K through 24K), a fineness (such as 585, 750, 916, 999), or a mass percent, and the tool updates the other two fields instantly using the canonical formula fraction = karat / 24. Twelve common karat presets load with a single click and show the conventional hallmark stamp (375, 585, 750, 916, and so on) alongside the exact math. The scrap gold panel takes an item weight in grams, troy ounces, pennyweight, or avoirdupois ounces, normalizes it to grams using exact conversion factors (1 ozt = 31.1034768 g, 1 dwt = 1.55517384 g, 1 oz = 28.349523125 g), and multiplies by the purity fraction to give pure gold mass. A spot price field (in any currency symbol you type) is normalized to a per-gram price using your chosen unit (per troy ounce, per gram, or per pennyweight), and the melt value plus an optional refiner payout percentage are calculated transparently with the exact equation shown on screen. No external API is called; you supply the current spot price from whichever source you trust. Karat and fineness are exact mathematical equivalents, but hallmarks round to standardized stamps (14K hallmarks as 585 even though 14/24 * 1000 = 583.33), and the reference table in the tool makes that distinction explicit so the math always matches what the stamp says. Useful for buying scrap gold, valuing jewelry before resale, comparing a refiner quote against melt, double-checking a 14K vs 18K vs 22K purchase, or any time you need to translate between a karat number and the percent of pure gold in an alloy. All math runs locally in your browser; weight, price, and purity figures are never uploaded.
Free to use. Works in your browser. No signup, no login.
Related tools
You may also like
Ring Size Converter
Convert between US, UK, EU, JP, and inner diameter or circumference.
Open tool
ConverterWeight Converter
Convert any weight between metric, imperial, and specialty units, all at once.
Open tool
CalculatorPercentage Calculator
Four percentage calculators: percent of, what percent, change, and discount.
Open tool
CalculatorMarkup Calculator
Bidirectional markup, margin, selling price, and cost math with currency-aware totals.
Open tool
CalculatorUnit Price Calculator
Compare cost per unit across sizes and packs to spot the best value.
Open tool
CalculatorDiscount Calculator
Sale price from stacked percent and amount off discounts, with optional tax and reverse mode.
Open tool