The mass–radius relation for polytropes is introduced and analyzed. The Newtonian Lane–Emden equation is derived analytically. Known analytic solutions are discussed. The famous Chandrasekhar mass is obtained as a solution of the Lane–Emden equation. Corrections to the equation of state for white dwarfs are pointed out by estimating the Coulomb corrections for a lattice of nuclei immersed in a sea of electrons. The different layers of a typical white dwarf and the typical sizes are worked out in detail. Thermal effects for the mass relation are examined. Finally, astrophysical observations of white dwarfs are shown and discussed in terms of the overall composition of white dwarfs and the resulting mass–radius relation.