This paper reports measurements of RDX and PETN sublimation rate in air. For both explosives the initial samples were prepared by precipitation from solution. For RDX a continuous thin film is obtained, while PETN samples were constituted of small, well separated, single crystals. The sublimation process was monitored using a quartz crystal microbalance (QCM). It is demonstrated that a quantitative description of the sublimation rates can be obtained using molecular diffusion equations in the surrounding air. A quantitative description is limited by the large discrepancy of the reported vapor pressure of these explosives in the literature. An additional obstacle in the accuracy of these predictions is the limited data related to vapor-in-air diffusion coefficients. The results reported herein allow us to determine the most relevant vapor pressure source among those reported in the literature and the most probable diffusion coefficient values.