In the domain of air filtration, the pressure drop across filtering medium represents, together with the retention efficiency the principal measures of filter performance. Theoretical prediction of the pressure drop . is essential, especially in case of design of new filters. The Pich formula is widely used for prediction of the pressure drop across a fibrous medium in terms of medium structural parameters and fluid properties. This paper presents a comprehensive investigation of this formula on the basis of experimental measurements of the pressure drop across various types of fibrous media and comparison of the test results with the theoretical prediction by Pich for different values of air flow rate. Analysis of results and conclusions are included.