How do you convert 1.2 g to 600 mg?

Answer 1

That's a lot like asking "How do you convert 1 foot to 6 inches?"

It can't be done, because 1.2 g is not the same as 600 mg, and it never will be

unless you cut it in half and throw half of it away.

1 g = 1,000 mg

1.2 g = 1,200 mg

600 mg = 0.6 g