  The desired result of magnetic anisotropy investigations is the determination
of value(s) of various anisotropy constant(s). This is sometimes difficult,
especially when the precise knowledge of saturation magnetization is required,
as it happens in ferromagnetic resonance (FMR) studies. In such cases we
usually resort to `trick' and fit our experimental data to the quantity called
\emph{anisotropy field}, which is strictly proportional to the ratio of the
searched anisotropy constant and saturation magnetization. Yet, this quantity
is scalar, simply a number, and is therefore of little value for modeling or
simulations of the magnetostatic or micromagnetic structures. Here we show how
to `translate' the values of magnetic anisotropy constants into the complete
vector of magnetic anisotropy field. Our derivation is rigorous and covers the
most often encountered cases, from uniaxial to cubic anisotropy.
