  A magnetic skyrmion is a topological object consisting of an inner domain, an
outer domain, and a wall that separates the two domains. The skyrmion size and
wall width are two fundamental quantities of a skyrmion that depend sensitively
on material parameters such as exchange energy, magnetic anisotropy,
Dzyaloshinskii-Moriya interaction, and magnetic field. However, there is no
quantitative understanding of the two quantities so far. Here, we present
general expressions for the skyrmion size and wall width obtained from energy
considerations. The two formulas agree almost perfectly with simulations and
experiments for a wide range of parameters, including all existing materials
that support skyrmions. Furthermore, it is found that skyrmion profiles agree
very well with the Walker-like 360\textdegree{} domain wall formula.
