  The finite sum of the squares of the Mie coefficients is very useful for
addressing problems of classical light scattering. An approximate formula
available in the literature, and still in use today, has been developed to
determine a priori the number of the most significant terms needed to evaluate
the scattering cross section. Here we obtain an improved formula, which
includes the number of terms needed for determining the scattering cross
section within a prescribed relative error. This is accomplished using extended
precision computation, for a wide range of commonly used size parameters and
indexes of refraction. The revised formula for the finite number of terms can
be a promising and valuable approach for efficient modeling light scattering
phenomena.
