The use of empirical formulas to predict penetration depths of projectiles in concrete is discussed in the report. An existing empirical equation is compared with experimental data from the literature, and the limitations of the empirical equation are discussed. Further, modifications and limitations for the used formula are given to consider projectiles with a length to diameter ratio between 6 and 10, and with a calibre head radius between 2 and 6. The modified model gives a fair agreement with the existing penetration data from the literature.