The use of applications on mobile devices has reached historic levels. Using the System Usability Scale (SUS), data were collected on the usability of applications used on two kinds of mobile platforms-phones and tablets-across two general classes of operating systems, iOS and Android. Over 4 experiments, 3,575 users rated the usability of 10 applications that had been selected based on their popularity, as well as 5 additional applications that users had identified as using frequently. The average SUS rating for the top 10 apps across all platforms was 77.7, with a nearly 20-point spread (67.7-87.4) between the highest and lowest rated apps. Overall, applications on phone platforms were judged to be more usable than applications on the tablet platforms. Practitioners can use the information in this article to make better design decisions and benchmark their progress against a known universe of apps for their specific mobile platform.