10k vs 14k vs 18k gold: what changes with each karat, in numbers

The three alloys side by side

Metal value is gold content times spot, $141.74 per gram of pure gold at build time. Hardness is Vickers, from published alloy tables for yellow alloys; nickel white golds run harder, 160 to 200 HV, and pure gold is about 25 to 30 HV.

Price: what you pay and what comes back

Retail jewelry sells at a multiple of its metal, and the multiple does not change much with karat, so the same ring costs roughly 28% more in 18k than in 14k and roughly 29% less in 10k, on the metal alone. Labor and margin are the same whichever alloy is poured, which is why the cheapest pieces are where 10k concentrates: on a $150 chain the gold is a small share of the price whatever the karat, and dropping to 10k saves the seller money it may or may not pass on.

Coming back the other way, a scrap buyer pays for gold content and nothing else. A 5 gram 18k band returns $531.50 at melt today, the same band in 14k $414.60, in 10k $295.50. So the share of the purchase price that survives as metal is highest for 18k and lowest for 10k, and a 10k piece bought at a mall markup has the worst buy-to-scrap ratio of the three. None of that matters for a piece worn for life; it matters for a piece that might be sold, given away or melted.

Durability: harder is not tougher

Every metal added to gold hardens it, so the ladder runs the way people expect: 18k yellow is about 125 to 140 Vickers, 14k yellow 140 to 160, 10k around 145 and, in some recipes, higher. In hand terms, a 14k band picks up fewer scratches than an 18k one over the same year, and 18k prongs need checking more often. All three clear the 100 to 120 HV that a prong needs to hold a stone; pure 24k does not, which is why it is not made into rings.

Hardness is only half of durability. The alloy metals that harden gold are also the ones that react. Copper and silver tarnish and leave the green or dark marks explained on the skin discoloration page; the more of them, the more of that, so 10k tarnishes more readily than 14k and 14k more than 18k, which barely does. Chlorine is the other side: pool and hot tub water attacks the alloy metals, and the low-karat and nickel white alloys are the ones that crack at stressed points and solder joints after many hours in it. So 10k scratches least and corrodes most; 18k scratches most and corrodes least; 14k sits in the middle on both counts, which is the real reason it is the default.

Color and skin

• Yellow. 18k is the deep, warm yellow of European and Indian jewelry; 14k is a shade lighter and slightly brassier; 10k is paler still and can look slightly green or red depending on the recipe. Side by side the difference is obvious; alone, most people cannot name the karat by color.
• White. The whitening metal in 10k and 14k white gold is usually nickel, and the cheaper the piece the more likely. Palladium white gold, the nickel-free version, is far more common at 18k. Anyone who itches from earrings should read the nickel page before buying white gold of any karat.
• Rose. More copper for the pink, so 14k rose is pinker than 18k rose and marks acidic skin a little more readily. 10k rose is the most red and the most reactive of the everyday alloys.

Skin reactions to gold itself are rare at any karat. Reactions to 10k and 14k are reactions to nickel in white alloys, or to copper marking, both explained on the colors page.

14k, 14kt, 14K, 585, 583 and KP: the same metal

The abbreviations confuse more people than the metallurgy. K, kt and ct all abbreviate karat, and 14K, 14kt and 14 ct on a piece of jewelry mean the same 58.5% gold; the British spell it carat and use the same word for gemstone weight. 585 is the same fraction written in parts per thousand, the European style. 583 is 14/24 worked out exactly, 0.58333, and was the US and Soviet marking before 585 became standard; a 583 piece is 14k by any test. 14KP means plumb, exactly 14/24 with no tolerance used.

Tolerance is the one place the letters matter for money. The FTC guides allow a piece without solder to be three parts per thousand under its mark and a piece with solder seven parts under, so a lawful 14K can assay at 578. A KP mark promises the full 585. Buyers pay by assay, not by stamp, so the difference is a fraction of a percent, but it explains why a buyer's tester can read a lawful 14K as a hair under 14k. The stamp decoder covers the letters that mean a layer rather than solid metal.

How to tell 14k from 18k in your hand

1. Read the stamp with a loupe; 585 or 14K against 750 or 18K settles it on an honestly marked piece.
2. Compare color against a known piece: 18k is visibly deeper yellow next to 14k, though neither can be judged alone.
3. Weigh for size. 14k yellow sits at 12.9 to 13.6 grams per cubic centimeter, 18k at 15.2 to 15.6, 10k at 11.3 to 11.6. A density check, dry weight over displaced water, separates all three; the method is on the testing page.
4. Acid, if you must. A touchstone streak that survives the 14k acid and dissolves under the 18k acid is 14k. It marks the piece and needs care.

What does not work: bite, magnet, or looking at the shine. Plated pieces pass every surface test, which is why the density check matters for anything unmarked.

Which karat to buy, by piece

The straight answer on 10k: it is real gold, it is the hardest of the three, and it is worth buying when the piece is yellow, worn hard, and bought at a price that reflects the metal it lacks. It is the wrong buy for white gold, for skin that reacts, for anything meant to be resold, and for anything that goes in a pool. The karat calculator shows the grams of gold and dollars in any piece before you decide.

Questions people ask