Gold Purity Calculator

What a karat actually measures

A karat is a fraction with a fixed denominator of 24. Pure gold is 24 parts out of 24, so every karat mark is simply karat divided by 24. That single line of arithmetic drives everything on this page: 22K is 22/24 = 91.67% gold, 18K is 18/24 = 75%, 14K is 14/24 = 58.3% and 10K — the legal minimum that can be sold as gold in the United States — is 10/24 = 41.7%. In the UK, 9K (37.5%) is legal and common, which is why a British "gold" chain often weighs the same as an American one but carries far less metal value.

Do not confuse the karat of gold with the carat of a gemstone. A diamond carat is a unit of mass equal to 0.2 grams. Gold karat is a purity ratio and has no weight meaning at all. A 22K, 10-gram bangle and a 14K, 10-gram bangle weigh the same and are worth very different sums.

Worked example: a 10 g 22K bangle, start to finish

Take a 22K bangle weighing 10 grams, with 24K trading at 85 per gram in your currency.

Step 1 — purity: 22 / 24 = 0.91666, so 91.67% gold.
Step 2 — pure gold content: 10 g x 0.91666 = 9.167 g of fine gold. The other 0.833 g is copper, silver or zinc and is worth close to nothing.
Step 3 — fineness: 916 parts per thousand, which is why the hallmark reads 22K916.
Step 4 — melt value: 9.167 g x 85 = 779.17.

Now compare the shop price. If the same bangle is ticketed at 950, the gap of roughly 171 is the making charge plus tax — about 22% over metal. That is within the normal band but worth negotiating; on a plain, machine-made piece there is little craft to pay for.

The same weight in other karats

Hallmarks: reading the stamp instead of trusting the seller

A hallmark is an independent assay office's statement of fineness, not a manufacturer's claim. In India, BIS hallmarking has been mandatory for gold jewellery since 2021 and carries three marks: the BIS logo, the purity grade (22K916, 18K750, 14K585) and a six-character HUID that can be checked in the BIS Care app. In the UK, the Assay Offices of London, Birmingham, Sheffield and Edinburgh stamp a sponsor's mark, a millesimal fineness number such as 750, and the office's town mark; anything sold as gold above 1 gram must be hallmarked. The United States has no compulsory hallmarking regime — the National Gold and Silver Stamping Act only requires that any stamp applied be accurate, so a "14K" mark is the maker's own assertion backed by law rather than a test.

Practical consequence: in a US shop, if the piece is unmarked or you doubt the mark, ask for an XRF scan. It is non-destructive, takes seconds and most serious buyers have the machine on the counter. Acid testing is cheaper but scratches the item and only reads the surface, which is exactly where a plated fake hides its lie.

Buying and selling with the numbers in hand

When buying, insist on three separate figures: the day's rate per gram, the net gold weight after deducting stones and any lac or resin filler, and the making charge as a percentage or a flat sum. A quote that bundles them into one number is a quote you cannot check. Gross weight on a stone-set piece can overstate the gold by 20% or more, and you should never pay the gold rate on the weight of a ruby.

When selling, expect less than the melt figure this calculator shows. Refiners and pawnbrokers typically pay 70% to 90% of melt for scrap, because they carry the refining cost and the price risk between your counter and their smelter. Jewellery bought at retail therefore has to survive a double haircut — the making charge you paid on the way in, and the buyer's margin on the way out. Coins and bars avoid most of that, which is why bullion and jewellery are genuinely different purchases even at identical purity.

Limits of this calculator

The output is a metal-content estimate, not an appraisal. It assumes the stated karat is truthful and that the weight you enter is gold only, so gemstones, clasps in a different alloy, hollow tube construction and enamel will all inflate the result. It also ignores craftsmanship, brand premium and antique value, which for a signed piece can exceed the metal value many times over. For anything unusual, use the number here as your floor and get a professional valuation before you sell.