Nuclear sizes are expressed in a unit named:

Nuclear dimensions and radii are extremely small, typically on the order of $10^{-15}\text{m}$. This length scale is expressed using the unit Fermi (also called femtometer, denoted as $\text{fm}$), where:
$$1\text{Fermi}=10^{-15}\text{m}$$

In comparison, Angstrom ($\text{A˚}$) equals $10^{-10}\text{m}$ and is commonly used for atomic dimensions. Newton is the unit of force, and Tesla is the unit of magnetic flux density.