Gold karat converter

A gold karat converter maps one purity scale onto the others so jewelers, appraisers, students, and buyers stop mixing 18K stamps with 750 fineness marks and percent purity claims. Enter a non-negative purity value and a unit—karat (zero to twenty-four), millesimal fineness in parts per thousand (zero to one thousand), or percentage (zero to one hundred)—and the tool returns all three equivalents, the pure-gold fraction, a short English summary, and step-by-step substitution lines. Hallmark reading, melt calculations, scrap buy sheets, and classroom purity problems all need the same deterministic arithmetic.

Karats, fineness, and percent: three scales for the same purity

Gold jewelry purity is the fraction of pure gold mass in an alloy, expressed in three common scales that are linearly related. The karat (also spelled carat in some jewelry markets, not to be confused with gemstone carat mass) divides pure gold into twenty-four parts: twenty-four karat is pure gold, eighteen karat is eighteen twenty-fourths pure, fourteen karat is fourteen twenty-fourths, and so on down to low-karat alloys used in some regions.

Millesimal fineness states parts of pure gold per thousand parts of alloy: one thousand is pure, seven hundred fifty is the common European stamp for eighteen karat, five hundred eighty-five for fourteen karat, and three hundred seventy-five for nine karat. Percentage purity is simply that fraction times one hundred, so pure gold is one hundred percent, eighteen karat is seventy-five percent, and nine karat is thirty-seven point five percent.

The internal hub of this converter is the pure-gold fraction f between zero and one: f equals karats divided by twenty-four, fineness divided by one thousand, or percent divided by one hundred. Values strictly greater than the pure-gold cap for the source unit—more than twenty-four karat, more than one thousand fineness, or more than one hundred percent—are rejected because they cannot describe a real gold alloy under these definitions. Negative values are also rejected.

Practical tips, common stamps, and when to use this landing

Prefer sending bare numbers for value when you control the client; string numbers are accepted only when they match a strict finite numeric pattern without unit symbols glued to the digits—put the scale in the unit field instead.

Classic classroom and trade pairs to verify by hand: eighteen karat equals seven hundred fifty fineness and seventy-five percent; fourteen karat equals five hundred eighty-three point three repeating fineness (rounded to twelve decimals here) and about fifty-eight point three percent; twenty-two karat equals about nine hundred sixteen point six six seven fineness; nine karat equals three hundred seventy-five fineness and thirty-seven point five percent; twenty-four karat, one thousand fineness, and one hundred percent are pure gold on all three scales.

Round-trip checks are straightforward: convert from karat to the published fineness and percent fields, then re-enter those magnitudes with the matching unit and confirm you recover the original karat within the published rounding. Stay inside non-negative pure-gold caps so the solver never has to invent super-pure alloys.

This landing targets people searching for a gold karat converter, karat to fineness, eighteen karat purity percent, millesimal gold stamp, or parts-per-thousand gold online; it is not a gold-price calculator, not a scrap melt yield estimator that needs mass and spot price, and not a gemstone carat-to-gram mass tool. Prefer this capability when you already have one purity number and unit and need the other scales plus step strings; if you need monetary valuation, combine purity with mass and a price feed elsewhere.