Lost-Wax Metal Calculator

In lost-wax casting, metal replaces the wax model exactly, so the wax weight tells you how much metal you need. Enter the wax weight and choose the metal; the calculator applies the density ratio and adds an allowance for sprues and losses.

Lost-wax metal

Include the wax sprues if they are attached
Casting waxes are often about 0.9 to 1.0
Extra metal so the mould fills fully

How it works

The metal fills the same volume the wax took up. Volume = wax weight ÷ wax density, so the metal weight = wax weight × (metal density ÷ wax density). This ratio is why casters often multiply the wax weight by a fixed number for each metal.

Casters add extra metal for the sprues, the button (the reservoir of metal that feeds the mould) and small losses. The allowance percentage covers this.

Worked example

A 50 g wax model cast in bronze, with wax at 0.93 g/cm³ and bronze at about 8.8 g/cm³, has a ratio of about 9.5. The casting holds about 473 g of bronze, and with a 15% allowance you would melt about 544 g.

Good to know

  • If your wax model already has its sprues attached, weigh it with them and use a smaller allowance.
  • Densities vary with the alloy, so check the figure from your metal supplier if you can.
  • Hollow casts made over a core use less metal than a solid wax of the same outer size. Weigh the wax as it will be invested.

Frequently asked questions

How do I convert wax weight to bronze weight?

Multiply the wax weight by the bronze density divided by the wax density. With typical values, that is roughly 9 to 10 times the wax weight.

Why do I need extra metal?

The sprues and the button must fill too, and some metal is lost. Extra metal makes sure the mould fills completely.

Does this work for Dhokra casting?

The principle is the same: metal replaces the wax. Dhokra pieces are built over a clay core, so weigh only the wax layer if you can.

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