The present paper provides the spectral solution of the Reynolds'film lubrication equation for finite length journal bearing which is an exact solution for infinite series expansion. Due to the bearing intrinsic symmetries mainly related to the geometry and flow field, the relevant 2nd order 2D quasi-linear partial differential equation in the rectangular domain with periodic and homogenous boundary conditions has been solved through suitable sinusoidal eigenfunctions which proved to be complete orthonormal systems over the integration domain. The spectral solution has been used to compute the performance of bearings with aspect ratio in the proximity of one that represents a condition far from the typical approximations of "long" and "short" bearing. The comparison between the "exact" solution and the approximated ones confirms that the approximated solutions do not provide neither an effective estimation of the performance nor a conservative one. Finally, a more refined field of applicability of the "long" and "short" bearing approximations has been identified through the comparison of their results with the "exact" performance provided by the spectral solution.
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