Several parameters can affect the level of damage of a concrete structure in case of hard, non-deformable missile impact. We carried out a series of finite element impact simulations validated by real experimental data to reveal the most important combination of parameters. Our numerical results show that the penetration depth and the perforation limit thickness can be obtained as a power-law function of the impact factor, a dimensionless number characterizing the impact. These formulae are simple, dimensionless, and can be effectively applied in case of a wide range of input parameters. We also found a simple formula based on the impact factor to determine the minimum target thickness required to achieve the penetration depth corresponding to an infinite half-space as the target. Beyond this minimum target thickness, the consequences of the impact do not depend on the target thickness.