How massive is a Neutron Star compared to its physical size?

It packs the mass of perhaps one or two suns into a sphere only about the size of a city.

Neutron stars represent an extreme state of matter density achieved after a supernova when the progenitor star's core mass is sufficient to collapse the material but not great enough to form a black hole. These exotic objects are built almost entirely of neutrons pressed together under immense pressure. Consequently, they achieve extraordinary density, housing the mass equivalent of one or two solar masses compressed into an incredibly small volume, typically comparable to the dimensions of a major terrestrial city. This confinement results in objects with incredibly strong magnetic fields and often very rapid rotational rates.