18K to 22K table
| 18K weight | 24K gold to add | 22K gold made | Same gold as |
|---|---|---|---|
| 1 g | 2.00 g | 3.00 g | 0.82 g 22K |
| 5 g | 10.00 g | 15.00 g | 4.09 g 22K |
| 10 g | 20.00 g | 30.00 g | 8.18 g 22K |
| 20 g | 40.00 g | 60.00 g | 16.36 g 22K |
| 50 g | 100.00 g | 150.00 g | 40.91 g 22K |
| 100 g | 200.00 g | 300.00 g | 81.82 g 22K |
Raising 18K to 22K
To raise purity you add 24K gold: added gold = weight × (0.9167 − 0.75) ÷ (1 − 0.9167). That is two grams of pure gold for every gram of 18K: 10 g of 18K needs 20.00 g of 24K and ends up as 30.00 g of 22K.
Because so much gold has to be added, goldsmiths rarely upgrade 18K. The usual route is to exchange the 18K piece for its value and buy 22K.
How much 22K is your 18K worth?
By gold content, 18K is worth 18 ÷ 22 of the same weight of 22K: 10 g of 18K contains as much gold as 8.18 g of 22K. An exchange offer close to that, minus the deduction, is a fair one.
Why some jewellery is 18K
18K (hallmark 750) is harder than 22K, so it holds diamonds and other stones more securely and is used for most stone-set, white gold and rose gold pieces. A lower gold content per gram is the trade-off.
Calculated with karat ÷ 24 (22K = 91.67%). Hallmarks round slightly differently (916, 750, 585); switch the calculator to the hallmark basis to match a buyer who prices by the stamp.
Frequently asked questions
How much pure gold do I add to 10 g of 18K to make 22K?
20.00 g of 24K gold, giving 30.00 g of 22K. The formula is weight × (22/24 − 18/24) ÷ (1 − 22/24).
How many grams of 22K is 10 grams of 18K?
8.18 g by gold content (10 × 18 ÷ 22).
Is 18K gold real gold?
Yes. 18K is 75% pure gold (hallmark 750); the remaining 25% is alloy such as silver, copper, palladium or nickel, which also sets its colour.