The Internet is all pervasive now. From its humble beginnings in the military five decades ago, the Internet has evolved into a dynamic medium that allow people to interact, collaborate and share information. In the U.S., more and more people are using the Internet than ever before. According to a 2009 PEW study (Rainie 2010), 74% of adults (ages 18 and older) use the Internet at home or some other location, compared to 48% in the year 2000. From this it follows that page views, which is the measure of website activity and are the number of distinct web pages served to a web user (Bhat, Bevans et al. 2002), are not indicative of the number of unique online users accessing the website because users can access the website from multiple locations. Therefore, to estimate reach, the proportion of online users who visited the website, we have to account for the duplication of website visitations from multiple locations. This estimation task is at the heart of this study and analysis. In this study, we estimate duplication of website visitations to popular websites in the U.S. from a RDDrecruited online panel in which consented panel members install software (a.k.a. meter) on their home and work computers as part of their membership in the panel. The software passively tracks their online and click stream behaviors at both home and work locations. We use multiple modeling approaches to study duplication of website visitations and along the way observe patterns in duplications across various demographic cohorts. In addition, we juxtapose these behavioral-based estimates against survey data, one that is obtained from an online opt-in panel. We discuss the findings from the study and conclude with recommendations for future research.