  We derive a simple formula for the real-space chirality of twisted bilayer
graphene that can be related to the cross-product of its sheet currents. This
quantity shows well-defined plateaus for the first remote band as function of
the gate voltage which are approximately quantized for commensurate twist
angles. The zeroth plateau corresponds to the first magic angle where a sign
change occurs due to an emergent $C_6$-symmetry. Our observation offers a new
definition of the magic angle based on a macroscopic observable which is
accessible in typical transport experiments.
