  Dirac electrons in graphene are to lowest order spin 1/2 particles, owing to
the orbital symmetries at the Fermi level. However, anisotropic corrections in
the $g$-factor appear due to the intricate spin-valley-orbit coupling of chiral
electrons. We resolve experimentally the $g$-factor along the three orthogonal
directions in a large-scale graphene sample. We employ a Hall bar structure
with an external magnetic field of arbitrary direction, and extract the
effective $g$-tensor via resistively-detected electron spin resonance. We
employ a theoretical perturbative approach to identify the intrinsic and
extrinsic spin orbit coupling and obtain a fundamental parameter inherent to
the atomic structure of $^{12}$C, commonly used in ab-initio models.
