A key component in the test and evaluation of bioaerosol detectors is the unit of measure used to describe the distributed bioaerosol. We examine two existing units of measure, Agent Containing Particles per Liter of Air (ACPLA), and Biologically Active Units per Liter of Air (BAULA). We conclude that ACPLA is an insufficient unit of measure that provides little useful information about the bioaerosol. While BAULA corrects many of the issues present in ACPLA, calculation of BAULA is extremely difficult as it requires knowledge of a number of variables that are currently unavailable. Therefore, we propose a new unit of measure, Total Agent per Liter of Air with particle size distribution (TALAp). TALAp contains the two most important variables for evaluating biodetectors: the amount of agent present and the particle size distribution. Thus, TALAp allows for more accurate and reproducible testing of biodetectors. Furthermore, TALAp can be implemented in sealed test chambers using existing referee equipment and is directly comparable to legacy ACPLA data. While some testing procedures may need to be augmented to measure TALAp in breeze tunnel and field testing, these new procedures are relatively simple to implement and will pay additional dividends to the test and evaluation community.