  Neutron stars radiate in a broad band spectrum from radio wavelengths up to
very high energies. They have been sorted into several classes depending on
their respective place in the $P-\dot{P}$ diagram and depending on
spectral/temporal properties. Fundamental physical parameters such as their
characteristic age and magnetic field strength are deduced from these primary
observables. However this deduction relies mostly on interpretations based on
simple vacuum or force-free rotating dipole models that are unrealistic. In
this paper, we show that the computation of the stellar surface magnetic field
is poorly estimated or even erroneous if multipolar components and particle
loading are neglected. We show how quadrupolar magnetic field and monopolar
winds alter field estimates and characteristic ages in the $P-\dot{P}$ diagram.
Corrections brought by general relativity are also discussed. We derive some
important parameters of pulsar physics such as the wind Lorentz
factor~($\gamma$) times the pair multiplicity~($\kappa$) to be around
$\gamma\,\kappa \approx 10^8-10^{10}$. Therefore, the standard magnetodipole
radiation losses formula must be used with caution to reckon neutron star
surface magnetic fields and related secular evolution parameters. Depending on
models we found that all field strengths, both for magnetars and for pulsars
lie below the quantum critical value of $B_{\rm c} \approx 4.4\cdot 10^9$~T.
