maximum distance from origin (float precision)

Ok, so players can travel up to about ~12km from origin in many directions. I believe I would need CM accuracy (player is about 1.5m in height) to produce desirable effects. My research on floating points has led me to believe that floats have ~7.2 decimal places of precision. 12,000.01 has seven digits, and would have cm accuracy, is this assumption correct? I have seen people claim that float precision has been the cause of issues in multiple cases, some claiming around 20km, others around 40km, and I saw one guy post a quote from unity reference saying something along the lines of 99km should be fine, but a warning will generate and issues arise past that. I have not seen this in the reference myself, he did not post a link.

Could someone clarify this for me? is my world too big to have players moving accurately at such distances? If not, could i push it to 20km safely? That is the biggest I could imagine ever using. I want to know the limits before I wing it with trial and error.