  Observations indicate that the convective cores of stars must ingest a
substantial amount of material from the overlying radiative zone, but the
extent of this mixing and the mechanism which causes it remain uncertain.
Recently, Anders et al. (2021) developed a theory of convective penetration and
calibrated it with 3D numerical hydrodynamics simulations. Here we employ that
theory to predict the extent of convective boundary mixing in early-type
main-sequence stars. We find that convective penetration produces enough mixing
to explain core masses inferred from asteroseismology and eclipsing binary
studies, and matches observed trends in mass and age. While there are remaining
uncertainties in the theory, this agreement suggests that most convective
boundary mixing in early-type main-sequence stars arises from convective
penetration. Finally, we provide a fitting formula for the extent of core
convective penetration for main-sequence stars in the mass range from $1.1-60
M_\odot$.
