Lost Wax Casting Weight Calculator
Calculate the metal weight needed for lost wax casting based on wax model weight and metal type.
Lost wax casting (also called investment casting) is one of the oldest metalworking techniques, dating back over 5,000 years to Mesopotamia. The process involves creating a wax model, encasing it in a plaster-like investment, burning out the wax, and pouring molten metal into the cavity.
The Weight Conversion Formula
Metal weight = Wax weight x (Metal density / Wax density) + Button weight
Where:
- Wax density (injection wax) = ~0.97 g/cm^3
- Button weight = the extra metal that solidifies in the sprue button (typically 1.5–3x the casting weight)
Metal Density Table
| Metal | Density (g/cm^3) | Conversion Factor (from wax) | Melting Point |
|---|---|---|---|
| Fine Silver (999) | 10.49 | 10.81 | 961°C (1,762°F) |
| Sterling Silver (925) | 10.36 | 10.68 | 893°C (1,640°F) |
| 10K Yellow Gold | 11.57 | 11.93 | 876°C (1,609°F) |
| 14K Yellow Gold | 13.07 | 13.47 | 829°C (1,524°F) |
| 18K Yellow Gold | 15.45 | 15.93 | 882°C (1,620°F) |
| 24K Gold (999) | 19.32 | 19.92 | 1,064°C (1,947°F) |
| Platinum (950) | 20.10 | 20.72 | 1,768°C (3,214°F) |
| Brass (yellow) | 8.50 | 8.76 | 927°C (1,700°F) |
| Bronze | 8.80 | 9.07 | 950°C (1,742°F) |
| Copper | 8.96 | 9.24 | 1,085°C (1,985°F) |
The conversion factor = metal density / wax density (0.97).
Worked Example — Sterling Silver Ring
Wax model weight: 3.2 grams. Metal conversion factor for sterling silver: 10.68. Casting weight = 3.2 x 10.68 = 34.2 grams of sterling silver.
Button allowance (2x casting weight): 34.2 x 2 = 68.4 grams. Total metal needed: 34.2 + 68.4 = 102.6 grams.
The button (the solidified metal in the sprue cone) is recovered and re-melted for future castings. It is not wasted — but you need it in your crucible to fill the mold completely.
Sprue Design Affects Metal Usage
| Sprue Type | Button Multiplier | Use Case |
|---|---|---|
| Single main sprue | 2.0x casting weight | Simple rings, pendants |
| Tree with 3–5 pieces | 1.5x total casting weight | Small batch production |
| Tree with 6–12 pieces | 1.2x total casting weight | Efficient production casting |
Larger trees are more efficient because the button size does not increase proportionally with the number of pieces.
Flask Temperature Guide
| Metal | Flask Temperature Before Pour |
|---|---|
| Silver / Gold | 480–540°C (900–1,000°F) |
| Platinum | 700–815°C (1,300–1,500°F) |
| Brass / Bronze | 480–540°C (900–1,000°F) |
A flask that is too hot causes porosity (gas bubbles in the casting). A flask that is too cool causes incomplete filling and cold shuts.
Cost Estimation
Once you know the metal weight, multiply by the current spot price per gram to estimate material cost. Add 10–15% for refining losses over multiple casting cycles.