I am from NZ and find myself doing this. The difference is whether something is estimated or measured. If it’s a rough estimate, and the value doesn’t matter at

I am from NZ and find myself doing this. The difference is whether something is estimated or measured. If it’s a rough estimate, and the value doesn’t matter at all, I use inches. So “six inches” is more of a way of describing “about this much”. It’s deliberately imprecise.