grams and oz dont even measure the same thing. Gm is mass and Oz is weight, (which is mass divided by a rep..force of gravity)
There are about 5% of people who have any inkling of the difference between mass and weight (to where they could answer questions intelligently on what happens if there is no gravity).
Whether they are living under the imperial system or metric system makes no difference.
For all intents and purposes, most Earthlings use mass and weight interchangeably.
In Newtonian mechanics, "mass" has no independent meaning of substance, really. It is simply a book-balancing concept used in equations. It is "resistance to acceleration," whatever the **** that really means.
Since F=M x A, it must be true (mathematically) that M = F/A. So, the less an object accelerates when subjected to the same uniform force, the more mass it has. In theory.
Resistance to acceleration roughly corresponds to "inertia," but nobody has ever been able to satisfactorily explain the origin and mechanisms of inertia.
All you really end up with is circular definitions and proposition which are true by virtue of definition, i.e., tautologies.