Wax Pattern Weight Calculator
Calculate the casting alloy weight needed from wax pattern weight using wax and alloy densities.
About this calculator
This calculator converts a weighed wax pattern into a volume (Wax Volume = Wax Pattern Weight divided by Wax Density), then multiplies that volume by Alloy Density to get the metal weight needed to fill the same space -- the same volume of a denser alloy simply weighs more. Wax Density and Alloy Density both move Alloy per Pattern, but in opposite directions: a higher Wax Density means the weighed wax represents a smaller true volume (so less alloy fills it), while a higher Alloy Density means that same volume weighs more once cast. Sprue Length and Sprue Diameter add a separate cylindrical volume (also converted at Alloy Density) to Sprue Weight, but neither changes Alloy per Pattern itself, which is calculated from the pattern alone.
Alloy densities vary widely by class: base-metal alloys (Ni-Cr or Co-Cr) run roughly 7-8 g/cc, palladium-silver alloys roughly 10.5-11 g/cc, and high-noble dental gold alloys roughly 15-18 g/cc -- notably lower than pure gold's 19.3 g/cc, since dental gold alloys are cut with silver, copper, palladium, or platinum rather than cast as pure metal. The 20% Button Reserve is a fixed planning margin for the sprue button and material lost in casting, not a measured shrinkage or waste figure specific to any alloy.
Medical Disclaimer
This calculator is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about your health. Never disregard professional medical advice or delay seeking it because of results from this tool.
Inputs
Results
Alloy per Pattern
15.66 g
Total Alloy Needed
19.38 g
How to Use This Calculator
- Weigh the wax pattern on a lab scale and enter the Wax Pattern Weight (g).
- Enter the Wax Density (typically 0.9-1.0 g/cc) and the Alloy Density for your casting metal.
- Enter the Sprue Length and Sprue Diameter to include the sprue channel weight.
- Set the number of Patterns on Tree if casting multiple units.
- Read off Alloy per Pattern, Button Reserve, and Total Alloy Needed (g) to prepare the crucible charge.
How the result changes with Wax Density
| Wax Density | Alloy per Pattern | Total Alloy Needed |
|---|---|---|
| 0.5 | 29.76 g | 36.3 g |
| 0.71 | 20.9 g | 25.66 g |
| 1.42 | 10.48 g | 13.16 g |
| 1.5 | 9.92 g | 12.49 g |
What each input means
- Wax Pattern Weight
- Weight of the wax pattern on a lab scale.
- Wax Density
- Density of the pattern wax (typically 0.9-1.0 g/cc).
- Alloy Density
- Density of casting alloy (high-noble gold alloy ~15-18, Pd-Ag ~11, base metal ~7-8).
- Sprue Length
- Length of the sprue channel.
- Sprue Diameter
- Diameter of the sprue former.
- Patterns on Tree
- Number of wax patterns sprued to the casting tree.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersWax Pattern Weight = 1.2, Wax Density = 0.95, Alloy Density = 12.4, Sprue Length = 8 = 6 input(s) provided
- Calculate Alloy per PatternAlloy per Pattern15.66 = 15.66
- Calculate Total Alloy NeededTotal Alloy Needed19.38 = 19.38
- Calculate Wax VolumeWax Volume1.263 = 1.263
- Calculate Sprue WeightSprue Weight0.49 = 0.49
Engine last updated . Checked against 1 independently-derived test — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why do Wax Density and Alloy Density move Alloy per Pattern in opposite directions?
Wax Volume is calculated by dividing Wax Pattern Weight by Wax Density, so a higher Wax Density implies the weighed wax occupies a smaller true volume -- less alloy is needed to fill it. Alloy Density then multiplies that volume back into a weight, so a denser alloy needs more metal to fill the same space. The two densities pull the result in opposite directions because one divides and the other multiplies.
Does Sprue Length change how much alloy the pattern itself needs?
No -- Sprue Length and Sprue Diameter only affect Sprue Weight, a separate cylindrical-volume calculation added on top. Alloy per Pattern is calculated purely from the wax pattern's own weight and density, independent of the sprue former's dimensions.
Is 19.3 g/cc the right density to enter for a gold casting alloy?
No -- 19.3 g/cc is pure gold's density, not a dental casting alloy's. Real high-noble dental gold alloys are cut with silver, copper, palladium, or platinum and typically run about 15-18 g/cc, so entering 19.3 would overstate the alloy weight needed. Use the density printed on your specific alloy's technical data sheet when possible.
What does the 20% Button Reserve actually account for?
It is a fixed planning margin this calculator adds on top of the calculated pattern and sprue weight, meant to cover the sprue button and typical material loss during casting. It is not a measured shrinkage or waste percentage specific to any alloy or casting technique -- labs with different casting methods may need more or less reserve in practice.
How does adding more Patterns on Tree change the total alloy needed?
All Patterns Weight and Total Alloy Needed both scale directly with Patterns on Tree, since each additional pattern adds the same per-pattern alloy and sprue weight to the running total. Doubling the number of patterns sprued to one tree roughly doubles the alloy charge required, all else equal.
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