In this report, we present a detection scheme that can be used to measure the absorption cross-section of the Nitrogen Vacancy (NV) centre, along with the results of an experimental implementation of this method. We also demonstrate how we quantify the number of NV centres in a crystal by calculating the collection efficiency of our apparatus. We find that the absorption cross-section for 532 nm excitation, averaged over the possible orientations of the transition dipole moments is (0.95 +/- 0.25) x 10(-16) cm(2). This level of accuracy has not been achieved in previous investigations. (C) 2011 Elsevier B.V. All rights reserved.