I learned it in First Grade and nearly everyone I have talked to did as well, and I am in California which is rated as the #40 best state for public education, which puts me technically near the bottom. So unless someone happens to come from a state that is lower than California (10 states in descending order where last is worst: TN, FL, NC, OK, SC, AL, NM, NV, LA, or AZ), then chances are very tiny that they were not taught that basic fact in grade school, which was then repeatedly used in every science class afterwards.

American Public Education Rankings by State