Deep learning models for image classification have often used a resolution of $224\times224$ pixels for computational reasons. This study investigates the effect of image resolution on chest X-ray classification performance, using the ChestX-ray14 dataset. The results show that a higher image resolution, specifically $1024\times1024$ pixels, has the best overall classification performance, with a slight decline in performance between $256\times256$ to $512\times512$ pixels for most of the pathological classes. Comparison of saliency map-generated bounding boxes revealed that commonly used resolutions are insufficient for finding most pathologies.