Wax-to-Metal Casting Calculator

How It Works

Lost-wax investment casting replaces a wax model with metal that flows into the empty cavity. The metal fills the same volume the wax occupied, so the finished casting weighs the wax weight multiplied by the ratio of metal density to wax density. Casting wax is typically 0.95-1.0 g/cm³, so a 4 g wax pendant occupies about 4 cm³ — and 4 cm³ of sterling silver at 10.36 g/cm³ weighs 41.4 g.

The core formula:

Metal weight = Wax weight × (Metal density / Wax density)

Standard densities used in the tool are drawn from Tim McCreight's The Complete Metalsmith (Casting chapter) and Rio Grande's metal density reference (riogrande.com/technical-library):

• Sterling silver (92.5% Ag) — 10.36 g/cm³
• Fine silver (99.9% Ag) — 10.49 g/cm³
• 14K yellow gold — 13.07 g/cm³
• 18K yellow gold — 15.58 g/cm³
• Platinum (950) — 20.13 g/cm³
• Yellow brass — 8.47 g/cm³
• Phosphor bronze — 8.80 g/cm³
• Copper — 8.96 g/cm³
• Aluminum — 2.70 g/cm³
• Pewter — 7.30 g/cm³
• Zinc — 7.14 g/cm³

The casting yield — how much metal actually ends up in the piece rather than the sprue button and gates — depends on your sprue design. Typical yields from Ganoksin.com casting references run 60-80%: for every 100 g of metal poured into the flask, 60-80 g ends up as usable casting and the rest as sprue button and gates that need to be filed off and re-melted for the next pour. The calculator reports both the model-only weight and a suggested purchase amount that adds a sprue allowance.

Casting wax model weight comes from wax density (typically 0.95-1.0 g/cm³ for injection wax, 0.85-0.90 for carving wax); if you weigh the wax model on a jewelry scale the tool needs only that number, not a volume computation.

How to Use This Calculator

1. Weigh your wax model — a jewelry scale accurate to 0.01 g gives the model weight in grams.
2. Select wax type — injection wax (density ~0.98) or carving wax (density ~0.88) if you know it; otherwise use the default 0.95.
3. Choose target metal — from the 15+ named alloys in the built-in database, or enter a custom density in g/cm³.
4. Set number of castings — pouring multiple copies of the same model requires proportionally more metal.
5. Choose sprue allowance — the tool defaults to 30% additional metal for typical hand-sprue setups; drop to 20% for tightly-sprued professional trees or bump to 40% for beginners.
6. Read the results — model weight in metal, plus total purchase weight including sprue allowance and casting count.

Real-World Use Cases

Silver pendant

A jeweler has a 4 g wax pendant model. At sterling silver density 10.36 g/cm³ and wax density 0.98 g/cm³, the model in metal weighs 4 × (10.36 / 0.98) = 42.3 g. With a 30% sprue allowance and one casting, she needs about 55 g of sterling to fill the flask cleanly. Anything less risks a shrunk casting or an incomplete pour.

Bronze sculpture element

A sculptor casts a decorative brass door pull with a 45 g wax master in yellow brass (8.47 g/cm³, wax density 0.95). Model weight in metal: 45 × (8.47 / 0.95) = 401 g. Plus 30% sprue allowance = 521 g. Because the sculptor pours one at a time on a hand tree, she rounds up to 550 g to have a safety margin for any splash loss.

14K gold ring

A goldsmith has a 1.2 g wax ring model in 14K yellow (13.07 g/cm³, wax density 0.98). Model in metal: 1.2 × (13.07 / 0.98) = 16.0 g. Plus 30% sprue = 20.8 g of 14K needed to pour a clean casting. Because 14K yellow is expensive per gram (~$45/g at current spot), rounding up is a real cost consideration and the goldsmith opts for a tighter 20% sprue allowance to save 1.5 g.

Tips & Safety Notes

• Weigh the wax model with the sprue attached, then subtract the sprue's separate weight. Some sprue setups distort the model's apparent volume if not accounted for correctly.
• Match wax density to your actual wax type. Injection waxes and carving waxes differ enough (0.95 vs 0.88) that a 4 g model differs by 4-5% between them — enough to matter on high-alloy gold pours.
• Cast with fresh metal alloyed to spec. Repeatedly re-melted sprue can pick up oxygen and other contaminants that shift the density by 2-3%; blend fresh with reclaimed 50:50 for a stable alloy.
• Wear a respirator when investing and casting. Investment powder contains crystalline silica and metal fumes from high-temperature pours are toxic in short doses.
• Never pour hot metal into a mold with residual moisture. Water vapor in the flask converts to steam and can violently eject molten metal. Preheat the flask to at least 300 °C before pouring.

Limitations & What This Tool Cannot Do

• No sprue geometry. The tool reports the model weight in metal plus a percentage sprue allowance; it does not compute sprue weight from actual sprue rod dimensions. If your sprue design is unusual (multiple thin gates, a large central button), tune the percentage from experience.
• Alloy variation. Uses standard published density values for named alloys. Custom alloys, master alloys with different composition, or reclaimed sprue blended in can shift density by 2-4%. When precision is important (thin high-K gold pieces), weigh a small test casting and back-calculate the actual density.
• Volume-limited accuracy. Density is assumed uniform; scaled or hollow wax models with internal voids need volume measurement (water displacement) rather than weight-based conversion. Hollowed-out wax master patterns will over-report the metal weight in the calculator.

FAQ

How is metal casting weight calculated from a wax model?

Multiply the wax model's weight by the ratio of metal density to wax density. For a 4 g wax pendant with wax density 0.98 g/cm³ and sterling silver density 10.36 g/cm³, the metal weight is 4 × (10.36 / 0.98) = 42.3 g. The tool does this automatically once you enter the wax weight and select the target metal.

Why is the metal so much heavier than the wax model?

Metals are 8-20 times denser than casting wax. Sterling silver at 10.36 g/cm³ is 10.6× the density of typical injection wax (0.98 g/cm³), so a wax model weighing 4 g becomes 42 g of silver in the same volume. High-density metals like platinum (20.13 g/cm³) multiply the wax weight by more than 20×.

What is a sprue and does the calculator include sprue weight?

A sprue is the channel through which molten metal flows into the mold, plus the button at the base that holds excess metal. Sprue and button together typically add 20-40% to the total weight of metal poured. The calculator adds a configurable sprue allowance (default 30%) to the model weight when computing purchase quantities.

Can I use this for centrifugal casting as well as lost-wax investment?

Yes. The math is identical — you are filling the same wax-defined volume with metal, and both processes need the same amount of metal for the model itself. Centrifugal casting typically needs a slightly larger sprue button to provide the pressure head, so consider a 35-40% sprue allowance instead of the default 30%.

How much extra metal should I buy above the calculated amount?

Add 30% for a typical hand-sprue setup (the default), 20% for a tightly-sprued professional tree, or 40-50% for a beginner or complex piece with multiple gates. Any leftover sprue metal can be re-alloyed and cast again, but starting short causes an incomplete pour that ruins the piece.

Which metal is easiest for a beginner: silver, bronze, or brass?

Sterling silver is the most beginner-friendly for jewelry-scale work: it melts cleanly around 900 °C, casts predictably, and is affordable enough to practice with. Bronze and brass require higher temperatures (1000+ °C) and can zinc-fume during casting, which is toxic. Larger sculpture pieces are still commonly bronze because of scale and cost.

Related Tools

• Wood Shrinkage Calculator — Materials-lab sister tool
• Sheet Metal Bend Calculator — Metal-work-adjacent tool for another dimensional problem
• Ceramic Clay Shrinkage Calculator — Materials-lab sister tool for shrinkage-driven math

References

• Tim McCreight, The Complete Metalsmith, "Casting" chapter — investment casting basics and alloy density values
• Rio Grande metal density and casting-yield reference (riogrande.com/technical-library) — commercial alloy densities and sprue allowance guidelines
• Ganoksin.com casting technical library — sprue design and yield percentages

Reviewed by the Craft Calc Lab team on August 4, 2026.