How are si units used in the united states?

Mostly in science classes, science laboratories, and companies
that manufacture things for export to other countries.

SI units are used very little by the common people, for things that
are going to stay in the US.  This is one of last three countries in the
world that have not officially adopted the metric system. 

We are unique, along with those other two economic, industrial, and
scientific leaders of the world:  Liberia and Myanmar.