Crust Thickness of Neutron Stars from the Crust-Core Transition to the Density Bound

The solid crust of a neutron star is only about a kilometre thick, yet it carries the superfluid reservoir, the pinning sites and the elastic stresses that govern pulsar glitches. This study computes crust thickness across a stated mass-radius sequence from 1.0 to 2.1 solar masses using a relativistic thin-shell hydrostatic estimate anchored at a crust-core transition density of 1.3e17 kg per cubic metre and a transition pressure of 0.45 MeV per cubic femtometre. For a canonical 1.4 solar-mass star of radius 12.6 km the crust is 1.45 km thick, a fraction 0.115 of the radius. Thickness falls from 2.12 km at 1.0 solar masses to 0.91 km at 2.1 solar masses, a thinning factor of 0.43, because surface gravity grows faster than the pressure scale height shrinks the shell. The transition density sits a factor 1.34e-41 below the Aldred density bound of 9.72e57 kg per cubic metre on the neutron branch, so the density bound supplies no crust-scale number: crust structure is set entirely by nuclear and hydrostatic physics, and that negative result is stated plainly. This study is simulated and computed from stated assumptions; it is not a measurement.