One of the primary motivating factors of physics educators is to ensure a high level of conceptual understanding is achieved by their students. Furthermore it has been shown that success in physics and engineering courses is strongly related to students' spatial skills. Conceptual and spatial skills tests have been independently developed and reported in the literature as a measure of each of these competencies. In this study we examine correlations between spatial skills and conceptual understanding using two of these tests in order to determine the relationship, if any, between students' conceptual understanding of Newtonian mechanics and their spatial skills. Spatial skills and Conceptual understanding of physics are tested using the Purdue Spatial Visualisation Test of Rotations (PSVT:R) and the Force Motion Concept Evaluation (FMCE) respectively. Correlations between PSVT:R and FCME scores are presented along with significant gender biases in both test scores.