Gold Karat Alloy Mix Calculator
Calculate gold and base metal weights for any karat alloy.
Mix 24K gold with silver, copper, or palladium to create 18K, 14K, or 10K alloys for jewelry making.
Gold Karat Alloy Mix
Pure gold is 24-karat (24K) = 99.9% gold. Lower karats are alloys with other metals (silver, copper, palladium) for hardness, color, or cost reduction.
Karat to gold percentage:
| Karat | Gold % | Stamp |
|---|---|---|
| 24K | 99.9% | 999 |
| 22K | 91.7% | 916 |
| 18K | 75.0% | 750 |
| 14K | 58.3% | 585 |
| 10K | 41.7% | 417 |
| 9K | 37.5% | 375 (UK/Ireland) |
The mix formula: Gold needed = Final weight × Target gold % Alloy needed = Final weight × (1 - Target gold %)
To reduce karat (e.g., 24K → 14K): add base metal alloy. To raise karat (e.g., 14K → 18K): add 24K gold to existing 14K.
Color alloys (the “master alloy”):
| Gold Color | Composition |
|---|---|
| Yellow gold | 50% Ag + 50% Cu (or pure Cu for redder) |
| Rose gold | 80-90% Cu + 10-20% Ag |
| White gold (modern) | Pd + Cu + Ag (palladium is preferred) |
| White gold (older) | Ni + Cu + Zn (nickel allergic risk) |
| Green gold | 75-100% Ag |
Density of gold alloys:
- 24K: 19.3 g/cm³
- 22K: 17.7 g/cm³
- 18K yellow: 15.6 g/cm³
- 14K yellow: 13.1 g/cm³
- 10K yellow: 11.6 g/cm³
To raise karat (e.g., turn 14K into 18K): 14K is 58.3% gold. To raise to 18K (75%): Gold to add = (Existing 14K × 0.583) - (Final 18K weight × 0.75) / negative balance Or equivalent: melt and add gold until weight ratio of pure gold to total is 0.75.
Cost calculation: At spot price S per gram pure gold:
- 18K cost ≈ S × 0.75 + alloy cost ($0.20-1/g for base metals)
- 14K cost ≈ S × 0.583 + alloy cost
- 10K cost ≈ S × 0.417 + alloy cost
Hardness vs purity:
- 24K: very soft, easily scratched, used for investment / coins
- 22K: soft but workable; common in India / Asia for jewelry
- 18K: ideal balance of color, hardness, and value
- 14K: most durable for everyday wear; slightly less yellow
- 10K: hardest gold, but more alloy than gold
US legal minimum to be sold as “gold jewelry”: 10K EU legal minimum in many countries: 8K (333) or 9K (375) in UK
Practical tip: when mixing, weigh out gold to 0.01g precision. Even small gold-quantity errors shift karat noticeably — always verify final piece by acid test or XRF.