ELi5: Where did all the different units of measurement come from? And how did we get a uniformed decision on what is what?

Question

I’m thinking distance or weight. Where did a fathom or metre come from and how do I know that my kilo is the same as yours?

In: Mathematics

Answer 1

This is how we got the English mile. Before we had Scottish miles, Irish Miles, English miles. But now we all use the same mile.