Why is the diameter of the molecule 0.1nm? How to convert it? Conversion of microscopic length

Why is the diameter of the molecule 0.1nm? How to convert it? Conversion of microscopic length

This is calculated by the oil film method
Originally, these oil droplets have a certain volume v
Then it is laid on the water surface to form area s
There is d = V / s
The conversion is 0.1nm = 10 ^ (- 10) M