Casting Metal Weight Calculator
Convert the weight of a wax model into the weight of metal needed to cast it, using specific gravity — plus an allowance for the sprue and button.
How it works
Model metal = wax weight × (metal SG ÷ wax SG) · Total = model metal × (1 + sprue allowance%)
A wax model has the exact volume of the finished casting, so metal weight is just wax weight scaled by the ratio of their densities. Since 14K gold is roughly 14.5 times denser than wax, a 2 g wax turns into about 29 g of gold. Always cast extra to fill the sprue (the feed channel) and leave a button in the crucible, which is why a 10–20% allowance is added — you can refine and reuse that surplus.
Worked example
A 2 g wax cast in 14K gold: factor = 13.1 ÷ 0.9 = 14.6, so the model needs 2 × 14.6 = 29.1 g. With a 15% sprue-and-button allowance, melt about 33.5 g of gold.
Frequently asked questions
Why multiply by specific gravity?
The wax and the casting share the same volume. Weight is volume × density, so the metal weight is the wax weight scaled by how much denser the metal is than the wax.
What specific gravity should I use for wax?
Most injection and carving waxes are about 0.9. If you know your wax’s exact figure, enter it — a small change barely moves the result because the metal density dominates.
Do I lose the sprue metal?
No. The sprue and button are cut off and can be re-melted or refined for the next casting, so the allowance is working stock, not waste.
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This calculator is for educational purposes. Double-check important results before acting on them.