the calculation of the metal weight is straightforward and very
the volume you want to fill with metal is previously filled with
wax, therefore the volume to be filled remains the same.
If you know the density (sometimes referred to as specific gravity)
of the wax G(w) you're using and you measure the mass of your total
(button, main sprue, sprues and models) wax M(w) then the Volume is:
which is the same volume for the metal.
With the specific gravity of your metal G(m) and the mass of the
metal M(m) the Volume is:
For the volume to be filled remains the same the ratio of M(m)/G(m)M
equals (w)/G(w). Therefore the Mass M(m) of metal needed is:
This applies for all waxes and all metals.
The density of your waxes and metals you may obtain from your
supplier or calculate by yourself.