This article considers the practical conversion of droplet size spectra data from Particle Measurement Systems (PMS) optical array probe (temporal, or number-flux weighted, sampling) to Malvern laser diffraction (spatial, or number-density weighted, sampling). PMS data collected from two wind tunnels are compared with Malvern data collected from a third. The resulting transformation is applied to the historical USDA Forest Service droplet size distribution database (PMS measurements), in an effort to provide data consistent with the Spray Drift Tash Force droplet size distribution database found in AgDRIFT(R) (Malvern measurements).