There is a constant ratio between shock pressure loss and the velocity pressure corresponding to the mean velocity of flow. Shock pressure losses can be calculated from the following formula: P_s=XP_v, where P_sequals the total shock pressure loss in 2880 inches of water, P _vequals the velocity pressure, in inches of water corresponding to the mean velocity of flow (equals approx. (V/4,000)₂at standard air density of 0.075 lb/ft₃or 1.2 kg/m₃), and X equals an empirical factor or shock factor found by experiment. P_sand P _vare expressed in the same units and are equally affected by density. X is therefore independent of both the density and the units used and is the number of velocity pressures equivalent to the shock pressure loss.