Gold & Silver Alloy Calculator
Calculate fine-metal and master-alloy weights for a target batch, raise or lower an existing batch's fineness, or find the resulting fineness of mixing known batches. Runs entirely in your browser.
Runs in your browser: every calculation uses plain arithmetic; nothing is uploaded to or stored by JewelModel.
Alloy math for a casting workshop
Calculating fineness is a mass-balance problem: the total weight of pure precious metal in a batch cannot change just because it gets melted, mixed, or diluted. This calculator uses that identity directly, so raising and lowering fineness use the same underlying formula instead of two formulas that could drift out of sync.
It handles three everyday workshop tasks: working out how much fine metal and master alloy to weigh out for a target batch, adjusting an existing batch up or down to a new target fineness, and finding the resulting fineness when known batches are melted together.
Useful for
- Preparing 14K, 18K, or any other target fineness from fine gold and a master alloy
- Diluting a higher-fineness alloy down, or enriching a lower-fineness one up, to a specific target
- Working out the resulting fineness of melting sprues, buttons, or scrap of known composition together
How the calculations work
Every result comes from the same three formulas, taken directly from our full guide to gold alloy fineness.
- Target batch: fine-metal mass = target weight × (target fineness − master alloy fineness) ÷ (fine metal fineness − master alloy fineness).
- Adjust fineness: mass to add = starting weight × (target fineness − starting fineness) ÷ (additive fineness − target fineness).
- Mix known batches: resulting fineness = the weighted average of each batch's weight × fineness, divided by the total weight.
What this calculator does not do
The math is exact; real metal is not. Treat every result as a starting weight, not a finished batch.
- It assumes the fineness you enter for existing metal or scrap is accurate — a hallmark alone is not proof, especially for purchased or customer scrap.
- It does not account for melting losses, zinc volatilization on repeated remelting, or master-alloy-specific behavior.
- It does not replace XRF analysis or fire assay on the actual finished, homogenized batch.
How to use the calculator
Three modes; no account or upload required.
- Choose a calculation
Pick target-batch, raise/lower fineness, or mix-known-batches, depending on what you're preparing.
- Enter weights and finenesses
Use the actual measured fineness of your fine metal, master alloy, or scrap — not just its stamped karat.
- Verify before production
Use the result as your starting weight, then confirm the finished, homogenized batch with XRF or fire assay.
Alloy calculator FAQ
Is fineness the same as karat?
No, but they convert directly. Fineness is parts of pure metal per 1000; karat is parts pure per 24. 18K equals 750 fineness; 14K equals 583.33 fineness, though 585 is widely used as the practical jewelry standard.
Why not just weigh 58.5 g of fine gold for 100 g of 585 gold?
Because that assumes the fine gold is exactly 1000 fineness. Real fine gold is usually 999 or 999.9. Using the actual fineness in the formula avoids a small but, at production volume, financially real error.
Can I trust a hallmark on scrap or customer metal?
Not on its own. Old jewelry can contain solder, plating, repairs, or components of different fineness. Treat purchased or customer scrap as unverified until it is tested or refined, and test a homogenized sample rather than the surface of an old piece.
Does this calculator account for melting losses or zinc loss?
No. It calculates an exact starting mass balance. Real casting introduces small losses, and zinc in particular is volatile on repeated remelting, so always verify the finished, homogenized batch rather than trusting the calculation alone.
Is my data sent to JewelModel?
No. Every calculation runs in this browser tab using plain arithmetic; nothing is uploaded or stored.
More jewelry-making resources
Read the full alloy fineness guide, browse jewelry CAD files, or publish your own original models.
Read the full alloy fineness guide · Browse all jewelry models · Sell original 3D models