The Jc of a polycrystalline film was studied experimentally and modeled by a percolation calculation. The superconducting thin film was modeled as a single layer of grains so that current limitation was considered as a linear optimization problem. Since the degree of in plane a-axis texturing of the grains in in situ Y-Ba-Cu-0 thin films was known, the critical current densities in polycrystalline superconducting thin films could be calculated. Comparison of transport and SQUID critical current densities from the experimental data and the calculated values in terms of intragrain critical current density, gave the estimation of Jc reduction across the 45” grain boundary.