Making an Electrum Band

I have this idea for a handmade ring, and Im wondering if you could
help me out with the material weights Im going to need. I want to
make a plain band with electrum that I’ve made myself set with 8
3-4mm black diamonds flush set around the band in equal spaces. I’ve
got plenty of fine silver to use, but Im wondering how many grams of
pure gold will i need for an average size 12-12.5 mens style band in
a 50/50 or 60(gold)/40(silver) mix.

Thanks in advance!