How big is a neutron relative to a proton?
A neutron is about three times the size of a proton.
The relative atomic mass of a proton is 1 and is the same for the neutron.
Therefore, a logical assumption would be that they are the same size — and that is a good approximation.
According to recent theories, a proton is a thin positive ring with radius
A neutron is a thin positive ring with radius
Thus, a neutron is 3 times the size of a proton.