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A study was performed to calculate the loss coefficients for flow through thin grille shapes of various geometries. The grille shapes were stamped sheet sections with holes which caused highly separated flow when flow was applied normal to the surface. Two-dimensional and three-dimensional CFD models were first built of simple shapes and compared with known data. This provided information on mesh density and solution methods required to achieve accurate results. Next, symmetric models were built of a number of grille shapes. Loss coefficients were calculated for several Reynold’s numbers. As expected, loss coefficients were relatively independent of Reynold’s numbers. It was also found that loss coefficients depended to a large degree only on the percent area open to the flow. Thus it was possible to use a single curve to represent losses through the grille for a wide variety of shapes and air speeds. Experimental data were obtained in a wind tunnel for a subset of grille shapes. These results agreed well with the analytical solution.