>>12419922A neutron star is about three times the size of its own Schwarzschild radius. Earth has a schwartzchild radius of about 1cm. Therefore a sphere of neutron star matter ~6cm across (3cm in radius) should be roughly equivalent to the Earth in mass, IF you naively assumed that a black hole's density to mass ratio is linear (ie twice the mass, twice the volume). This is not the case, which is good, because otherwise with that density a typical neutron star with a 20 km diameter would have a mass of 2.96 x 10^17 Earths, and would out-mass all the non-dark-matter mass in the galaxy. Obviously this can't be true, which is where the fact that the density of a black hole's event horizon volume is inversely proportional to its mass comes into play.
Doing the math a different way, Earth has a total mass of about 6x10^24 kg, and neutron star matter has a density of ~10^17 kg/m^3. Therefore, you'd need 60 million cubic meters of neutron star to have an Earth's mass of material, which is a sphere ~486 meters across. This makes a lot more sense, because if you mashed ~333,000 of these Earth-mass spheres together, equivalent to the mass of the Sun, you'd have a sphere with a radius of ~17 km, which lines up pretty well with a lower mass neutron star (they shrink as they get more massive, crushing themselves more under their own gravity).
