Wax-to-Metal Casting Calculator

How It Works

Lost-wax (investment) casting converts a wax model into metal through a straightforward density ratio. The key insight: a wax model and its metal casting occupy the same volume, but metals are much denser than wax.

The Core Formula:

1. Calculate the volume of your wax model: volume = wax weight ÷ wax density
2. Multiply that volume by the target metal's density to get the required metal weight
3. Add a waste margin for sprues, the casting button, and finishing loss

Why density matters for jewelers: A ring that weighs 3g in wax will weigh about 32g in sterling silver and 48g in 18K gold. Knowing this before casting prevents ordering too little (or too much) precious metal.

How to Use

1. Weigh your wax model — use a precision scale (0.01g resolution for jewelry)
2. Select wax type — casting wax, carving wax, or injection wax (each has different density)
3. Choose target metal — from 18 metals including various gold karats
4. Set waste margin — 5% is typical; increase for complex pieces with many sprues
5. Check the comparison table — instantly see what the same piece weighs in other metals

Tips for Casters

• Weigh after spruing — include sprue wax in your measurement since that volume will also be filled with metal. The waste margin covers what you'll cut away.
• Account for the button — the button (metal reservoir at the top of the flask) uses significant metal. For small pieces, it can weigh more than the piece itself. The 5% default margin may not cover this; experienced casters often add the button weight separately.
• Injection vs. carving wax density — injection wax is denser (1.00 g/cm³) than carving wax (0.93 g/cm³). Using the wrong density introduces a 7% error in your metal estimate.
• Alloy composition matters — 18K gold density varies from 15.2 (rose) to 15.6 (yellow) to 16.0 (white) depending on alloy metals. This calculator uses standard formulations.
• Verify with test castings — for production runs, cast one piece first and weigh it to calibrate your waste margin for that specific design.

FAQ

How accurate is this calculation?

For solid pieces, accuracy is typically within 2-3% of actual cast weight. Hollow forms, pieces with thin walls, or complex internal structures may show larger variance due to investment (plaster) intrusion or incomplete fill during casting.

Should I weigh the sprues separately?

For maximum accuracy, yes. Weigh the complete wax tree (model + sprues + button former) and calculate metal needed for the whole tree. After casting, you'll recover most sprue metal as scrap for reuse.

What about shrinkage in casting?

Metals shrink slightly as they cool from liquid to solid (about 1.5-3% by volume for most jewelry metals). This is generally offset by the slightly oversized investment mold cavity (the plaster expands when heated). The net effect on weight is negligible.

Can I use this for large sculpture casting?

Yes, but for bronze sculpture casting the waste margins should be higher (10-15%) due to larger spruing systems, risers, vents, and more finishing loss. Also ensure your foundry uses the same alloy density you calculated with.

What if my wax is hollowed out?

Weigh the wax as-is. The calculator converts weight to volume, so a hollow wax model will produce the correct metal weight for the same hollow form. The metal casting will be hollow in the same places the wax was.

Related Tools

• Sheet Metal Bend Calculator — Calculate flat pattern lengths for metal fabrication
• Epoxy Resin Calculator — Similar volume-based material calculation for resin molds

Last reviewed: June 2026