Karat, fineness and milyem: 21, 875 and 999
What 21 karat means, how it relates to 875, a conversion table for every common fineness, and why a system should store the number rather than the name.
Karat and fineness are two ways of saying the same thing: how much of this alloy is pure gold. Karat divides the whole into twenty-four parts; fineness divides it into a thousand.
| Karat | Fineness | Pure gold | Common in |
|---|---|---|---|
| 24 | 999 | 99.9% | Bullion and investment |
| 22 | 916 | 91.6% | India and the Gulf |
| 21 | 875 | 87.5% | Egypt, the Levant, the Gulf |
| 18 | 750 | 75.0% | Europe and stone-set work |
| 14 | 585 | 58.5% | United States and Europe |
| 9 | 375 | 37.5% | United Kingdom |
The conversion, in one line
Fineness equals karat × 1000 ÷ 24. So 21 karat is 21 × 1000 ÷ 24 = 875, and 18 karat is 750.
Why a system stores the number, not the name
Because the name changes with the market and the number does not. What Cairo calls "21 karat" another market calls 875, and a third calls "875 touch". Storing the text "21K" means every calculation has to translate first — and the translation differs depending on who wrote it.
So ZahabFlow stores an integer from 1 to 1000 and displays it the way your market reads it: karat in Cairo, fineness in Dubai, touch where touch is used. One stored value, many presentations.
What this does to stock
Once fineness is a number, stock becomes addable. A hundred grams at 875 and fifty grams at 750 are not a hundred and fifty grams of one thing — they are 87.5 + 37.5 = 125 grams of pure gold. That figure, not the piece count, is what the shop actually owns.
Questions we are asked
Which is better to buy, 21k or 18k?
For saving, the higher fineness holds value closer to the metal. For stone-set jewellery 18k is preferred because it is harder and holds settings better.
Is 24 karat used in jewellery?
Rarely — it is very soft. It dominates bullion and investment coins.
What is "touch"?
A common name for fineness in some markets: "875 touch" means the same as 21 karat.