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

Lengths were usually based on body parts. A cubit for example was the distance from the elbow to the tip of the middle finger. Hands for height of horses is another. Area was usually agricultural. An acre was the average distance an ox could plow in a day. Carats for gemstones was apparently based on carob seeds.

Governments often codified standards for trade purposes. The rise of science demand even more uniformity and precision. The metric system or form ofnit was proposed in the 1670 and was officially standardized by the french republic in 1790.