  We consider a universal relation between moment of inertia and quadrupole
moment of arbitrarily fast rotating neutron stars. Recent studies suggest that
this relation breaks down for fast rotation. We find that it is still universal
among various suggested equations of state for constant values of certain
dimensionless parameters characterizing the magnitude of rotation. One of these
parameters includes the neutron star radius, leading to a new universal
relation expressing the radius through the mass, frequency, and spin parameter.
This can become a powerful tool for radius measurements.
