Fluid flow in porous media has received much attention in recent years because of its important role in a large variety of engineering and technical applications, such as filtration units, wastewater treatment, packed beds, and certain types of chemical reactors. The porosity is the most important property of a porous medium and it affects most of the physical properties of the medium. Semi-empirical modified equation for the porosity had been proposed depending on the parameters affecting the porosity for water flow through porous media for sphere particles of mono size packing system. The parameters affecting the porosity in the packed bed of sphere packing were found to be the particle diameters and bed diameter. Several types and kinds of packing materials with different sizes have been used in the packed bed such as Pea Gravel, Marbles, Glass Marbles, Plastic Marbles, Black Marbles, Clear Marbles, Acrylic balls and Glass spheres. The diameters of the packing materials used in this model are from the range of (0.2-0.89) cm, the porosity is from the range of (0.3-0.76), the bed diameters is from the range of (7.62-15.24) cm, velocity is from the range of (0.002 - 0.3) m/s, the pressure drop is from the range of (24.9–59097) Pa and the height of packing is from the range of (7.62 - 56) cm. The calculation results of the porosity modified equations have been compared with Furnas equation of porosity and with experimental results taken from documented literature data; the comparisons show a very good agreement between the porosity modified equation and experimental results.