The difference between 24K, 22K, 21K and 18K gold
What is the difference between 24K, 22K, 21K and 18K gold? How much pure gold each holds, why each is used for something different, and how the gram price of each karat is worked out from 24K — with a worked example.
A karat is not a quality grade or a brand. It is a ratio: how much of the piece is pure gold, and how much is other metals added to harden it and change its colour. Everything that follows from the karat — price, use, durability and resale value — comes from that ratio alone.
The four karats in one table
| Karat | Per thousand | Pure gold | Typical use |
|---|---|---|---|
| 24 | 999 | 99.9% | Bars, coins |
| 22 | 916 | 91.6% | Jewellery in the Gulf and India, bangles |
| 21 | 875 | 87.5% | Jewellery in Egypt, Saudi Arabia and most of the Gulf |
| 18 | 750 | 75.0% | Stone-set jewellery; Europe and Morocco |
Why is not all jewellery 24K?
Because pure gold is soft. A 24K ring bends and scratches in daily wear and does not hold a stone securely. The lower the karat, the more metal is added — mostly copper and silver — so the piece becomes harder and better at holding stones, and its colour changes: rose from more copper, white from other metals.
That is why bars are 24K — they are bought to be kept, not worn — and stone-set jewellery is often 18K, because stones need metal that grips them. Between the two sit 21K and 22K, the choice of markets that want a piece worn every day that still holds a high share of gold.
How the gram price of each karat is worked out
You start from the price of pure gold and multiply by the karat’s share. There are two common ways of doing this that give slightly different numbers, and it is worth knowing which your shop uses:
- By karat: 21K price = 24K price × 21 ÷ 24.
- Per thousand against 999: 21K price = 24K price × 875 ÷ 999, because "24K" on the market is 999 pure, not 1000.
Example: if 24K is — for illustration — 5,000 per gram:
| Karat | By karat (÷24) | Per thousand (÷999) |
|---|---|---|
| 24 | 5,000.00 | 5,000.00 |
| 22 | 4,583.33 | 4,584.58 |
| 21 | 4,375.00 | 4,379.38 |
| 18 | 3,750.00 | 3,753.75 |
The gap at 21K is more than four per gram. On a kilo of stock that is over four thousand — which is why the method must be written down and agreed in the shop, not left to each salesman.
The gram price is not the piece price
A gram of 18K is cheaper than a gram of 21K, but an 18K piece is not necessarily cheaper. The making charge on fine stone-set pieces is higher, and stones are added on top. Always compare the whole price: pure gold in the piece × rate, then making, then stones, then tax.
And when you sell it later
When you sell a used piece, a shop usually pays you the value of the pure gold in it at its buying price; the making charge is not returned. A 10 g piece at 21K holds 8.75 g of pure gold, a 10 g piece at 18K only 7.5 — so the difference in resale value follows the karat directly.
In the shop’s software
ZahabFlow stores fineness as parts per thousand — 999, 916, 875, 750 — because that number is what brings different karats into one account: pure gold. Each fineness has its own buying and selling rate, updated from the world price with the shop’s margin, or by hand.
Questions we are asked
Which karat is best?
None is best in every case. 24K is purest and suits bars; 21K and 22K suit everyday jewellery; 18K suits stone-set pieces. The best one is the one that fits the purpose.
Is 21K the same as 875?
Exactly: 21 ÷ 24 = 0.875, so 875 parts per thousand are pure gold.
Why do two shops quote different 21K prices on the same day?
Among other reasons: the method (÷24 or ÷999), each shop’s margin between buying and selling, and when the rate was last updated.
Is 18K real gold?
Yes. Three quarters of it is pure gold, and it is the usual karat for jewellery in Europe and many other markets.