Metal Alloy Mixing Calculator
Calculate metal alloy ratios for gold karat blending and custom jewelry.
Returns grams of fine metal and alloy for yellow, white, and rose gold recipes.
Jewelry alloy mixing requires precise calculations to achieve a target purity. The most common application is blending gold of different karats or mixing pure gold with base metals.
The Karat System: Pure gold is 24 karat (24K). Each karat represents 1/24th (4.167%) gold content.
- 24K = 99.9% gold
- 18K = 75.0% gold
- 14K = 58.3% gold
- 10K = 41.7% gold
Mixing Formula (two metals of different purities): To find how much of Metal A and Metal B to combine for a target purity:
Weight_A × Purity_A + Weight_B × Purity_B = Total_Weight × Target_Purity
If you know the total desired weight and one source purity: Weight_A = Total × (Target - Purity_B) / (Purity_A - Purity_B) Weight_B = Total - Weight_A
Worked Example: Making 10g of 14K gold from 24K and 10K:
- Target purity: 14/24 = 58.333%
- Metal A (24K): 100% gold
- Metal B (10K): 10/24 = 41.667% gold
- Weight_A = 10 × (58.333 - 41.667) / (100 - 41.667) = 10 × 16.667 / 58.333 = 2.86 g of 24K
- Weight_B = 10 - 2.86 = 7.14 g of 10K
Verification: (2.857 × 1.000) + (7.143 × 0.41667) = 2.857 + 2.976 = 5.833 g of pure gold. 5.833 / 10 = 58.33%, which is 14K confirmed.
Notice how little of the batch is fine gold. Making 14K out of 24K and 10K takes under three grams of the expensive metal per ten grams of finished alloy, because the 10K stock is already 42% gold and is doing most of the work. Buying scrap 10K rather than more fine gold is usually the cheaper route to a 14K batch, and it is why bench jewelers hoard their sweeps.
Common Alloy Compositions:
| Alloy | Gold | Silver | Copper | Other |
|---|---|---|---|---|
| 18K Yellow | 75% | 12.5% | 12.5% | none |
| 18K Rose | 75% | 2.8% | 22.2% | none |
| 18K White | 75% | none | none | 25% palladium or nickel |
| 14K Yellow | 58.3% | 14.2% | 27.5% | none |
| Sterling Silver | none | 92.5% | 7.5% | none |
Copper is what makes rose gold rose. Compare the two 18K rows: same gold content, same karat stamp, and the only difference is that the rose recipe moves almost all of the silver over to copper. That single swap is the whole color.
A note on what the calculator assumes. It treats karat as a straight fraction of 24, so 24K is taken as 100% gold. In practice “fine gold” is 99.9%, and refiners work to 999.9 for investment bars. The difference changes a 10-gram batch by about a hundredth of a gram, which is below what a jeweler’s scale resolves, so the simplification is safe. It stops being safe if you are assaying for hallmark: legal minimums are absolute, and a 14K piece that assays at 58.2% fails in a jurisdiction that requires 58.3%.
The calculator below uses the two-source mixing formula. Enter both source karats and your desired target.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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