  Determining the heavy-element accretion rate of growing giant planets is
crucial for understanding their formation and bulk composition. The solid
(heavy-element) accretion rate should be carefully modeled during the various
stages of giant planet formation and therefore, the planetary capture radius
must be determined. In some simulations that model the heavy-element accretion
rate, such as in N-body simulations, the presence of the gaseous envelope is
either neglected, or treated in an over-simplified manner. In this paper, we
present an approximation for the capture radius that does not require the
numerical solution of the stellar structure equations. Our approximation for
the capture radius works extremely well for various planetesimal sizes and
compositions. We show that the commonly assumed constant density assumption for
inferring the capture radius leads to a large error in the calculated capture
radius and we therefore suggest that our approximation should be implemented in
future simulations.
