The practical application of grids and lattices is extremely wide. However, their use results in additional resistance and energy losses in the flow. Selecting the type and mesh design is determined by its purpose and conditions of use. The article investigates a perforated plastic grid with varying degrees of permeability at the outlet of the conduit. We have experimentally determined the effect of mesh on the flow rates of the pressure pipe. Flow coefficient values were set in two ways: with constant and variable pressure. It is shown that the two methods for determining the rate coefficients are identical. We have calculated the drag coefficients of the grid. The influence of grid porosity on the numerical values of these coefficients has been studied. The calculated values are approximated by the degree of the dependence linking the drag coefficients to surface grids and linear porosity. The proposed dependencies have been compared with the data presented in the literature. The recommendations for setting the values of drag coefficients of the devices are given.