Is a gram customary or metric?
It is metric not customary because the usa doesnt use it
Doesn't it? Oh yes it is. Almost all of the rest of world does, I'll have you know!
And so do American engineers and scientists, especially when engaged in international projects.
In most of the world, there is no difference, because the metric system is the customary system. In a few isolated hold-out corners of the world, such as the USA, the English system is still customary. In those places, the main difference between the metric system and their customary system is that their customary system is a lot harder for their people to learn than the metric system would be.