`r_p = 0.8775 * 10^-15 m`

8.775E-16

This constant, `r_p`, defines the rms charge radius of a proton.  This constant for the rms charge of a proton is expressed in meters (m).

Notes

This constant, `r_p`, is specified with a standard uncertainty (standard deviation) of: 0.0051 E-15 m

The root mean square (rms) charge radius is used to measure the size of an atomic nucleus.  The distance is computed as a root mean square (rms) value because atoms and nuclei have no definite boundaries and thus it is appropriate to calculate a statistical model of the sphere of charge seen by the electrons.  The dimension of the charge effect which represents the size of the nuclei is derived from electron scattering.