Particle size is measured routinely in the pharmaceutical industry. ICH Q6A1 provides useful insight as to why, highlighting the potential for the particle size of an active pharmaceutical ingredient (API) to impact dissolution, solubility, and bioavailability and the processability, content uniformity, stability, and appearance of the drug product. However, closer examination of the relationship between particle size and these critical behaviours raises the issue of whether particle size is the most informative parameter to measure. This white paper explores why there is a strong argument for adding surface area measurements as a complementary technique to particle size measurements such as dynamic light scattering (DLS) and laser diffraction, in pharmaceutical formulation and manufacture and the benefits of doing this.